gag vs sicken

gag is a noun but sicken is not a noun.

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

As verbs, sicken is a hypernym of gag; that is, sicken is a word with a broader meaning than gag:

gag (noun)	sicken (noun)
restraint put into a person's mouth to prevent speaking or shouting
a humorous anecdote or remark intended to provoke laughter

gag (verb)	sicken (verb)
struggle for breath; have insufficient oxygen intake	get sick
make an unsuccessful effort to vomit; strain to vomit	make sick or ill
cause to retch or choke	cause aversion in; offend the moral sense of
make jokes or quips	upset and make nauseated
be too tight; rub or press
tie a gag around someone's mouth in order to silence them
prevent from speaking out