jerking off vs onanism

jerking off and onanism both are nouns.

Word	Noun	Adjective	Verb	Adverb
jerking off	Yes	No	No	No
onanism	Yes	No	No	No

As nouns, onanism is a hypernym of jerking off; that is, onanism is a word with a broader meaning than jerking off:

jerking off: slang for masturbation
onanism: manual stimulation of the genital organs (of yourself or another) for sexual pleasure

Other hypernyms of jerking off include masturbation.

jerking off (noun)	onanism (noun)
slang for masturbation	manual stimulation of the genital organs (of yourself or another) for sexual pleasure
	a method of birth control in which coitus is initiated but the penis is deliberately withdrawn before ejaculation