Suffix
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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.
A suffix used to form the comparative degree of adjectives and adverbs; as, warmer, sooner, lat(e)er, earl(y)ier.
Source: Webster's dictionary