The nasal infix is a reconstructed nasal consonant or syllable *⟨n(é)⟩ that was inserted (infixed) into the stem of a word in the Proto-Indo-European language, that has reflexes in several modern European languages. It served the inflectional purpose of forming tense.
In the Proto-Indo-European language (PIE), the nasal infix *⟨n(é)⟩ is one of several means to form the athematic present tense. It is inserted immediately before the last consonant of the zero-grade root.
The infix appeared as *⟨né⟩ in the forms where a full-grade stem would be expected, and as *⟨n⟩ in forms where zero-grade would be expected. For example, the PIE root *weik- "to win" would yield a nasal-infixed present stem *wi⟨né⟩k- ~ *wi⟨n⟩k-.
Since the linguistic ancestor of PIE is not known, there can only be speculations about the origins of the nasal infix. It has been suggested that it arose from a suffix (also related to *-neH- and *-neu-) which underwent metathesis.
Other present tense markers 
Besides the nasal infix, PIE employs a number of affixes to mark the present: *-u-, *-neu-, *-neH-, *-sḱe-, *-de-, and others. All in all, PIE has at least 18 ways to form the present tense. For many verbs, several of these presents can be reconstructed simultaneously. For example, Scottish Gaelic loisg "to burn" goes back to *l̥h₂p-sḱé-, a sḱe-present of the root *leh₂p- which is also the source of Ancient Greek λάμπειν (lámpein) "to shine" via its nasal present *l̥h₂⟨n⟩p-.
It is not clear why there were so many different types of present forms with no or little discernible differences in meaning. The authors of the Lexikon der indogermanischen Verben proposed that they were derived from a number of prior grammatical aspects with distinct (but lost) meanings.
Indo-European languages 
In Latin as well as other daughter languages, the *n was assimilated to m before labial consonants (b, p), and to ŋ, spelled n in Latin and γ in Ancient Greek, before velar consonants (g, k, qu). Latin rūpit "has broken" / rumpit "breaks", from *rup- / *ru⟨n⟩p-, is an example of the first case.
- vīcit "has won" / vincit "wins" (from the PIE verb above)
- contudit "has crushed" / contundit "crushes"
- scidit "has cut" / scindit "cuts"
Latin loanwords 
English and the other Germanic languages show only vestiges of the nasal infix. The only certain remaining example is English stand, with the past tense stood lacking the n. However, it can still be seen in some pairs of Latin loanwords:
- confuse – confound (Latin confundō)
- impact – impinge (Latin impingō, from in- + pangō)
- conviction – convince (Latin con-vincō)
|PIE||Reflexes in daughter languages (3rd person singular)|
|*l(e)ikʷ-||*li⟨n(e)⟩kʷ-||Latin||līquit [ˈliːkʷit]||linquit [ˈliŋkʷit]||leaves, quits|
|*sl(e)h₂gʷ-||*slh₂⟨n(e)⟩gʷ- (?‡)||Ancient Greek||ἔ-λαβε (é-labe)||λαμβάνει (lambánei)||takes|
†The Latin reflexes of the PIE aorist came to be used as the perfect.
‡It is uncertain whether *sleh₂gʷ- had a nasal infix already in PIE, since Greek λαμβάνω is only attested after Homer.
Slavic languages 
|This section may be confusing or unclear. Please help . In particular, which forms are these? How do they translate into English?. (February 2013)|
A nasal infix appears regularly in words
- inherited from Latin
- words in which the second syllable has an accented nu.
- canutus > cănút > cănúnt > cărunt (with secondary dissimilation)
- minutus > mănut > mănúnt > mărúnt (with secondary dissimilation)
- renuculus >rănúchi > rănúnchi >rărúnchi (with secondary dissimilation)
- manipulus >mănúchi >mănúnchi
- renuculus >rănúchi > rănúnchi >rărúnchi
- genuculus > genúchi > genúnchi
- Late Latin *aminaciare > améniț > améninț
In J. R. R. Tolkien's constructed language Quenya, the nasal infix forms the past tense of verbs ending in any consonant besides -m, -n, or -r. Thus, cen- "to see" has the past tense cen-në, but mat- "to eat" has not *mat-në but the metathesised ma⟨n⟩t-ë.
See also 
- Baldi, Philip (22 January 1999), The Foundations of Latin, Trends in Linguistics, Mouton de Gruyter, p. 372, ISBN 3-11-016294-6
- Rix, Helmut (2001), Lexikon der indogermanischen Verben (in German), Dr. Ludwig Reichert Verlag, p. 670, ISBN 3-89500-219-4
- Fortson, Benjamin W., IV (2004), Indo-European Language and Culture, Blackwell Publishing, p. 88, ISBN 1-4051-0316-7
- Milizia, Paolo (2004), "Proto-Indo-European Nasal Infixation Rule", Journal of Indo-European Studies 32: 337–359
- Rix (2001:14–20)
- Rix (2001:402)
- Rix (2001:36–37)
- Petschenig (1971:435)
- Rix (2001:510–511)
- Petschenig, Michael (1971), Der kleine Stowasser (in German), Vienna: Oldenbourg Schulbuchverlag, pp. 138, 442, 533
- Ringe (2006:78)
- Rix (2001:670, 547–548, 510–511)
- "confound". Dictionary.com Unabridged. Random House, Inc.
- Harper, Douglas. "impact". Online Etymology Dictionary.
- Harper, Douglas. "convince". Online Etymology Dictionary.
- Rix (2001:179, 406–407, 566, 316)
- Petschenig (1971:227)
- Petschenig (1971:298)
- Schäfer, Karl-Heinz; Zimmermann, Bernhard (1990), Taschenwörterbuch Altgriechisch (in German) (3 ed.), Munich: Langenscheidt, p. 271, ISBN 3-468-10031-0
- Vedabase: yunakti
- Fortson (2004:250)
- A. Reformatskij, An introduction to linguistics (Введение в языкознание), Moscow 1996
- Fauskanger, Helge Kåre. "Quenya Course", lesson 6.