gag vs howler

gag and howler both are nouns.

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

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

gag (noun)	howler (noun)
restraint put into a person's mouth to prevent speaking or shouting	a glaring blunder
a humorous anecdote or remark intended to provoke laughter	monkey of tropical South American forests having a loud howling cry
	a joke that seems extremely funny

gag (verb)	howler (verb)
struggle for breath; have insufficient oxygen intake
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