jacking off vs onanism

jacking off and onanism both are nouns.

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

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

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

Other hypernyms of jacking off include masturbation.

jacking 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	a method of birth control in which coitus is initiated but the penis is deliberately withdrawn before ejaculation