-er

from the GNU version of the Collaborative International Dictionary of English.

• 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.
• A suffix used to form the comparative degree of adjectives and adverbs.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• suffix no longer productive Suffix used to form the plural of a small number of English nouns.
• suffix added to a verb or imitative sound frequently; used to form frequentative verbs.
• suffix added to verbs person or thing that does an action indicated by the root verb; used to form an agent noun.
• suffix added to a noun denoting an occupation Person whose occupation is (the noun).
• suffix A name for a person or thing that is based on a number (with or without a noun).
• suffix slang Used to form nouns shorter than more formal synonyms.
• suffix informal One who enjoys.
• suffix derogatory Person who subscribes to a particular conspiracy theory or unorthodox belief.
• suffix more; used to form the comparative.
• suffix more; used to form the comparative.
• suffix Used to form slang or colloquial equivalents of words.
• suffix added to a proper noun Suffix denoting a resident or inhabitant of (the place denoted by the proper noun); used to form a demonym.
• suffix Suffix denoting residency in or around a district, area, or region.
• suffix person or thing connected with
• suffix added to a verb instance of (the verbal action); used to form nouns from verbs, especially in legal terms.