ER

ER or Er may refer to:

People

Er (biblical person), the eldest son of Judah in the biblical book of Genesis
Er, a character in Plato's Myth of Er
Èr, an ancient people inhabiting parts of what are now northern Armenia, northeast Turkey, southern Georgia, and northwest Azerbaijan
Nie Er (1912–1935), Chinese composer

-er, a suffix added to adjectives or adverbs to form a comparative (e.g. fast to faster)
-er, a suffix added to a verb to make it an agent noun (e.g. cut to cutter)
Oxford "-er", a suffix used to form words like rugger and footer
"er", a filler (linguistics)
Er (Cyrillic) (Р / р), a letter of the Cyrillic alphabet corresponding to the Latin letter "R"
Er, alternate spelling for Yer (Ъ / ъ), the hard-sign letter of the Cyrillic alphabet
Er., Hebrew abbreviation for 'Eruvin, the second tractate of Moed

Initialism for emergency room, a medical facility specializing in acute, emergency care, usually found in a hospital or other primary care center

$\epsilon _{r}$ , a representation for Relative static permittivity
Electrorheological (ER) fluid, a type of chemical suspension
Endoplasmic reticulum, a type of organelle in cell biology
Enantiomeric ratio, a concept in chemistry
Equine exertional rhabdomyolysis, a syndrome that damages muscle tissue in horses
Estrogen receptor, a type of protein molecule
Extraction ratio, a pharmacokinetic property
Symbol for chemical element Erbium on the periodic table