gag line vs laugh line

gag line and laugh line both are nouns.

Word	Noun	Adjective	Verb	Adverb
gag line	Yes	No	No	No
laugh line	Yes	No	No	No

As nouns, gag line and laugh line are synonyms defined as:

Other synonyms of gag line include punch line, tag line.

gag line (noun)	laugh line (noun)
the point of a joke or humorous story	the point of a joke or humorous story
	a wrinkle in the skin at the outer corner of your eyes