onanism vs jacking off

onanism and jacking off both are nouns.

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

As nouns, jacking off is a hyponym of onanism; that is, jacking off is a word with a more specific, narrower meaning than onanism:

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

Other hyponyms of onanism include self-abuse, self-stimulation, frottage, hand job, jerking off, wank.

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a method of birth control in which coitus is initiated but the penis is deliberately withdrawn before ejaculation