forming nouns, denoting:
somebody who does, produces, or uses something performs (the action specified)
cyclist
novelist
somebody who makes or produces (the thing specified)
somebody who plays (the musical instrument specified)
harpist
somebody who operates (the mechanical instrument or device specified)
motorist
somebody who specializes in or practises something (the art, science, skill, or profession specified)
geologist
ventriloquist
somebody who adheres to or advocates a (the doctrine, system, or code of behaviour specified)
socialist
royalist
hedonist
Calvinist
somebody who is prejudiced on grounds of
sexist
[Middle English -iste via French and Latin from Greek -istēs, from verbs ending in -izein -ize]