-er 1
suff.1. a. One that performs a specified action: swimmer.
b. One that undergoes or is capable of undergoing a specified action: broiler.
c. One that has: ten-pounder.
d. One that is associated or involved with: banker.
2. a. Native or resident of: New Yorker.
b. One that is: foreigner.
[Middle English, partly from Old English -ere (from Germanic *-ārjaz, from Latin -ārius, -ary), partly from Anglo-French -er (from Old French -ier, from Latin -ārius) and partly from Old French -ere, -eor; see -OR1.]