onanist vs wanker

onanist and wanker both are nouns.

Word	Noun	Adjective	Verb	Adverb
onanist	Yes	No	No	No
wanker	Yes	No	No	No

As nouns, wanker is a hyponym of onanist; that is, wanker is a word with a more specific, narrower meaning than onanist:

Other hyponyms of onanist include frotteur, jerk-off, tosser.

onanist (noun)	wanker (noun)
a person who practices masturbation	terms of abuse for a masturbator