Meaning of -ER in English

-ER

The termination of many English words, denoting the agent; -- applied either to men or things; as in hater, farmer, heater, grater. At the end of names of places, -er signifies a man of the place; as, Londoner, i. e., London man.

Webster's Revised Unabridged English Dictionary.      Пересмотренный полный словарь английского языка Webster.