joke vs gag

joke and gag both are nouns.

Word	Noun	Adjective	Verb	Adverb
joke	Yes	No	Yes	No
gag	Yes	No	Yes	No

As nouns, joke and gag are synonyms defined as:

joke and gag: a humorous anecdote or remark intended to provoke laughter

Other synonyms of joke include jape, jest, laugh.

As verbs, gag is a hyponym of joke; that is, gag is a word with a more specific, narrower meaning than joke:

Other hyponyms of joke include quip, arse around, fool, fool around, horse around, pun.

joke (noun)	gag (noun)
a ludicrous or grotesque act done for fun and amusement	restraint put into a person's mouth to prevent speaking or shouting
activity characterized by good humor	a humorous anecdote or remark intended to provoke laughter
a triviality not to be taken seriously
a humorous anecdote or remark intended to provoke laughter

joke (verb)	gag (verb)
act in a funny or teasing way	struggle for breath; have insufficient oxygen intake
tell a joke; speak humorously	make an unsuccessful effort to vomit; strain to vomit
	cause to retch or choke
	make jokes or quips
	be too tight; rub or press
	tie a gag around someone's mouth in order to silence them
	prevent from speaking out