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A pentagon is a five sided polygon. A regular pentagon has 5 equal edges and 5 equal angles.

In geometry, a polygon /ˈpɒlɪɡɒn/ is traditionally a plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed chain. These segments are called its edges or sides, and the points where two edges meet are the polygon's vertices (singular: vertex) or corners.

The word polygon comes from Late Latin polygōnum (a noun), from Greek πολύγωνον (polygōnon/polugōnon), noun use of neuter of πολύγωνος (polygōnos/polugōnos, the masculine adjective), meaning "many-angled". Individual polygons are named (and sometimes classified) according to the number of sides, combining a Greek-derived numerical prefix with the suffix -gon, e.g. pentagon, dodecagon. The triangle, quadrilateral and nonagon are exceptions, although the regular forms trigon, tetragon, and enneagon are sometimes encountered as well.

Greek numbers

Polygons are always named by prefixes from Greek numbers.

English-Greek numbers

English cardinal number	English ordinal number	Greek cardinal number	Greek ordinal number
one	first	hena	protos
two	second	dyo	deuteros
three	third	tria	tritos
four	fourth	tessera	tetartos
five	fifth	pente	pemptos
six	sixth	hexi	hektos
seven	seventh	hepta	hebdomos
eight	eighth	okto	ogdoös
nine	ninth	ennea	enatos
ten	tenth	deka	dekatos
eleven	eleventh	hendeka	hendekatos
twelve	twelfth	dodeka	dodekatos
thirteen	thirteenth	dekatria	dekatos tritos
fourteen	fourteenth	dekatessera	dekatos tetartos
fifteen	fifteenth	dekapente	dekatos pemptos
sixteen	sixteenth	dekahexi	dekatos hektos
seventeen	seventeenth	dekahepta	dekatos hebdomos
eighteen	eighteenth	dekaokto	dekatos ogdoös
nineteen	nineteenth	dekaennea	dekatos enatos
twenty	twentieth	eikosi	eikostos
twenty one	twentieth first	eikosi hena	eikostos protos
twenty two	twentieth second	eikosi dyo	eikostos deuteros
twenty three	twentieth third	eikosi tria	eikostos tritos
twenty four	twentieth fourth	eikosi tessera	eikostos tetartos
twenty five	twentieth fifth	eikosi pente	eikostos pemptos
twenty six	twentieth sixth	eikosi hexi	eikostos hektos
twenty seven	twentieth seventh	eikosi hepta	eikostos hebdomos
twenty eight	twentieth eighth	eikosi okto	eikostos ogdoös
twenty nine	twentieth ninth	eikosi ennea	eikostos enatos
thirty	thirtieth	trianta	triakostos
thirty one	thirtieth first	trianta hena	triakostos protos
thirty two	thirtieth second	trianta dyo	triakostos deuteros
forty	fortieth	saranta	tessarakostos
fifty	fiftieth	penenta	pentekostos
sixty	sixtieth	hexenta	hexekostos
seventy	seventieth	hebdomenta	hebdomekostos
eighty	eightieth	ogdonta	ogdoëkostos
ninety	ninetieth	enenenta	enenekostos
hundred	hundredth	hekato	hekatostos
hundred ten	hundredth tenth	hekaton deka	hekatostos dekatos
hundred twenty	hundredth twentieth	hekaton eikosi	hekatostos eikostos
two hundred	two hundredth	diakosia	diakosiostos
three hundred	three hundredth	triakosia	triakosiostos
four hundred	four hundredth	tetrakosia	tetrakosiostos
five hundred	five hundredth	pentakosia	pentakosiostos
six hundred	six hundredth	hexakosia	hexakosiostos
seven hundred	seven hundredth	heptakosia	heptakosiostos
eight hundred	eight hundredth	oktakosia	oktakosiostos
nine hundred	nine hundredth	enneakosia	enneakosiostos
thousand	thousandth	chilia	chiliostos
two thousand	second thousandth	dyo chiliades	deuteros chiliostos
three thousand	third thousandth	tria chiliades	tritos chiliostos
four thousand	fourth thousandth	tessera chiliades	tetartos chiliostos
five thousand	fifth thousandth	pente chiliades	pemptos chiliostos
six thousand	sixth thousandth	hexi chiliades	hektos chiliostos
seven thousand	seventh thousandth	hepta chiliades	hebdomos chiliostos
eight thousand	eighth thousandth	okto chiliades	ogdoös chiliostos
nine thousand	ninth thousandth	ennea chiliades	enatos chiliostos
ten thousand	tenth thousandth	deka chiliades	dekatos chiliostos
twenty thousand	twentieth thousandth	eikosi chiliades	eikostos chiliostos
thirty thousand	thirtieth thousandth	trianta chiliades	triakostos chiliostos
forty thousand	fortieth thousandth	saranta chiliades	tessarakostos chiliostos
fifty thousand	fiftieth thousandth	penenta chiliades	pentekostos chiliostos
sixty thousand	sixtieth thousandth	hexenta chiliades	hexekostos chiliostos
seventy thousand	seventieth thousandth	hebdomenta chiliades	hebdomekostos chiliostos
eighty thousand	eightieth thousandth	ogdonta chiliades	ogdoëkostos chiliostos
ninety thousand	ninetieth thousandth	enenenta chiliades	enenekostos chiliostos
hundred thousand	hundredth thousandth	hekato chiliades	hekatostos chiliostos
two hundred thousand	two hundredth thousandth	diakosia chiliades	diakosiostos chiliostos
three hundred thousand	three hundredth thousandth	triakosia chiliades	triakosiostos chiliostos
million	millionth	chilia chiliades	chiliostos chiliostos

Systematic polygon names

To construct the name of a polygon with more than 20 and fewer than 100 edges, combine the prefixes as follows.

Tens		Ones		final suffix
		1	-hena-	-gon
20	icosi- (icosa- when alone)	2	-di-
30	triaconta-	3	-tri-
40	tetraconta-	4	-tetra-
50	pentaconta-	5	-penta-
60	hexaconta-	6	-hexa-
70	heptaconta-	7	-hepta-
80	octaconta-	8	-octa-
90	enneaconta-	9	-ennea-

Extending the system up to 999 is expressed with these prefixes.

Polygon names

Ones		Tens		Twenties		Thirties+		Hundreds
		10	deca-	20	icosa-	30	triaconta-	100	hecta-
1	hena-	11	hendeca-	21	icosi-hena-	31	triaconta-hena-	200	dihecta-
2	di-	12	dodeca-	22	icosi-di-	32	triaconta-di-	300	trihecta-
3	tri-	13	trideca-	23	icosi-tri-	33	triaconta-tri-	400	tetrahecta-
4	tetra-	14	tetradeca-	24	icosi-tetra-	40	tetraconta-	500	pentahecta-
5	penta-	15	pentadeca-	25	icosi-penta-	50	pentaconta-	600	hexahecta-
6	hexa-	16	hexadeca-	26	icosi-hexa-	60	hexaconta-	700	heptahecta-
7	hepta-	17	heptadeca-	27	icosi-hepta-	70	heptaconta-	800	octahecta-
8	octa-	18	octadeca-	28	icosi-octa-	80	octaconta-	900	enneahecta-
9	ennea-	19	enneadeca-	29	icosi-ennea-	90	enneaconta-

List of n-gons by Greek numerical prefixes

List of n-gon names

Sides	Names
1	henagon	monogon
2	digon
3	trigon	triangle
4	tetragon	quadrilateral
5	pentagon
6	hexagon
7	heptagon
8	octagon
9	enneagon	nonagon
10	decagon
11	hendecagon
12	dodecagon
13	tridecagon
14	tetradecagon
15	pentadecagon
16	hexadecagon
17	heptadecagon
18	octadecagon
19	enneadecagon
20	icosagon
21	icosikaihenagon	icosihenagon
22	icosikaidigon	icosidigon	icosadigon
23	icosikaitrigon	icositrigon	icosatrigon
24	icosikaitetragon	icositetragon	icosatetragon
25	icosikaipentagon	icosipentagon	icosapentagon
26	icosikaihexagon	icosihexagon	icosahexagon
27	icosikaiheptagon	icosiheptagon	icosaheptagon
28	icosikaioctagon	icosioctagon	icosaoctagon
29	icosikaienneagon	icosienneagon	icosaenneagon
30	triacontagon
31	triacontakaihenagon	triacontahenagon	tricontahenagon
32	triacontakaidigon	triacontadigon	tricontadigon
33	triacontakaitrigon	triacontatrigon	tricontatrigon
34	triacontakaitetragon	triacontatetragon	tricontatetragon
35	triacontakaipentagon	triacontapentagon	tricontapentagon
36	triacontakaihexagon	triacontahexagon	tricontahexagon
37	triacontakaiheptagon	triacontaheptagon	tricontaheptagon
38	triacontakaioctagon	triacontaoctagon	tricontaoctagon
39	triacontakaienneagon	triacontaenneagon	tricontaenneagon
40	tetracontagon		tessaracontagon
41	tetracontakaihenagon	tetracontahenagon	tessaracontahenagon
42	tetracontakaidigon	tetracontadigon	tessaracontadigon
43	tetracontakaitrigon	tetracontatrigon	tessaracontatrigon
44	tetracontakaitetragon	tetracontatetragon	tessaracontatetragon
45	tetracontakaipentagon	tetracontapentagon	tessaracontapentagon
46	tetracontakaihexagon	tetracontahexagon	tessaracontahexagon
47	tetracontakaiheptagon	tetracontaheptagon	tessaracontaheptagon
48	tetracontakaioctagon	tetracontaoctagon	tessaracontaoctagon
49	tetracontakaienneagon	tetracontaenneagon	tessaracontaenneagon
50	pentacontagon		pentecontagon
51	pentacontakaihenagon	pentacontahenagon	pentecontahenagon
52	pentacontakaidigon	pentacontadigon	pentecontadigon
53	pentacontakaitrigon	pentacontatrigon	pentecontatrigon
54	pentacontakaitetragon	pentacontatetragon	pentecontatetragon
55	pentacontakaipentagon	pentacontapentagon	pentecontapentagon
56	pentacontakaihexagon	pentacontahexagon	pentecontahexagon
57	pentacontakaiheptagon	pentacontaheptagon	pentecontaheptagon
58	pentacontakaioctagon	pentacontaoctagon	pentecontaoctagon
59	pentacontakaienneagon	pentacontaenneagon	pentecontaenneagon
60	hexacontagon		hexecontagon
61	hexacontakaihenagon	hexacontahenagon	hexecontahenagon
62	hexacontakaidigon	hexacontadigon	hexecontadigon
63	hexacontakaitrigon	hexacontatrigon	hexecontatrigon
64	hexacontakaitetragon	hexacontatetragon	hexecontatetragon
65	hexacontakaipentagon	hexacontapentagon	hexecontapentagon
66	hexacontakaihexagon	hexacontahexagon	hexecontahexagon
67	hexacontakaiheptagon	hexacontaheptagon	hexecontaheptagon
68	hexacontakaioctagon	hexacontaoctagon	hexecontaoctagon
69	hexacontakaienneagon	hexacontaenneagon	hexecontaenneagon
70	heptacontagon		hebdomecontagon
71	heptacontakaihenagon	heptacontahenagon	hebdomecontahenagon
72	heptacontakaidigon	heptacontadigon	hebdomecontadigon
73	heptacontakaitrigon	heptacontatrigon	hebdomecontatrigon
74	heptacontakaitetragon	heptacontatetragon	hebdomecontatetragon
75	heptacontakaipentagon	heptacontapentagon	hebdomecontapentagon
76	heptacontakaihexagon	heptacontahexagon	hebdomecontahexagon
77	heptacontakaiheptagon	heptacontaheptagon	hebdomecontaheptagon
78	heptacontakaioctagon	heptacontaoctagon	hebdomecontaoctagon
79	heptacontakaienneagon	heptacontaenneagon	hebdomecontaenneagon
80	octacontagon		ogdoecontagon
81	octacontakaihenagon	octacontahenagon	ogdoecontahenagon
82	octacontakaidigon	octacontadigon	ogdoecontadigon
83	octacontakaitrigon	octacontatrigon	ogdoecontatrigon
84	octacontakaitetragon	octacontatetragon	ogdoecontatetragon
85	octacontakaipentagon	octacontapentagon	ogdoecontapentagon
86	octacontakaihexagon	octacontahexagon	ogdoecontahexagon
87	octacontakaiheptagon	octacontaheptagon	ogdoecontaheptagon
88	octacontakaioctagon	octacontaoctagon	ogdoecontaoctagon
89	octacontakaienneagon	octacontaenneagon	ogdoecontaenneagon
90	enneacontagon		enenecontagon
91	enneacontakaihenagon	enneacontahenagon	enenecontahenagon
92	enneacontakaidigon	enneacontadigon	enenecontadigon
93	enneacontakaitrigon	enneacontatrigon	enenecontatrigon
94	enneacontakaitetragon	enneacontatetragon	enenecontatetragon
95	enneacontakaipentagon	enneacontapentagon	enenecontapentagon
96	enneacontakaihexagon	enneacontahexagon	enenecontahexagon
97	enneacontakaiheptagon	enneacontaheptagon	enenecontaheptagon
98	enneacontakaioctagon	enneacontaoctagon	enenecontaoctagon
99	enneacontakaienneagon	enneacontaenneagon	enenecontaenneagon
100	hectogon	hecatontagon	hecatogon
120	hecatonicosagon	dodecacontagon
200	dihectagon		diacosiagon
300	trihectagon		triacosiagon
400	tetrahectagon		tetracosiagon
500	pentahectagon		pentacosiagon
600	hexahectagon		hexacosiagon
700	heptahectagon		heptacosiagon
800	octahectagon		octacosiagon
900	enneahectagon		enneacosiagon
1000	chiliagon
2000	dichiliagon
3000	trichiliagon
4000	tetrachiliagon
5000	pentachiliagon
6000	hexachiliagon
7000	heptachiliagon
8000	octachiliagon
9000	enneachiliagon
10000	decachiliagon	myriagon
20000	icosachiliagon
30000	triacontachiliagon
40000	tetracontachiliagon
50000	pentacontachiliagon
60000	hexacontachiliagon
70000	heptacontachiliagon
80000	octacontachiliagon
90000	enneacontachiliagon
100000	hecatochiliagon
200000	diacosiachiliagon
300000	triacosiachiliagon
1000000	hecatommyriagon	megagon
∞	apeirogon

See also

• Platonic solid
• Dice

References

• NAMING POLYGONS
• Benjamin Franklin Finkel, A Mathematical Solution Book Containing Systematic Solutions to Many of the Most Difficult Problems, 1888

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• Polygons
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