Meaning of ER in English

ER

Function: adjective suffix or adverb suffix

Etymology: Middle English -er, -ere, -re, from Old English -ra (in adjectives), -or (in adverbs); akin to Old High German -iro, adjective comparative suffix, Latin -ior, Greek -i ō n

― used to form the comparative degree of adjectives and adverbs of one syllable <hott er > <dri er > and of some adjectives and adverbs of two or more syllables <complet er > <beautifull er >

Merriam Webster Collegiate English Dictionary.      Merriam Webster - Энциклопедический словарь английского языка.