gridlock vs snarl-up

gridlock and snarl-up both are nouns.

Word	Noun	Adjective	Verb	Adverb
gridlock	Yes	No	No	No
snarl-up	Yes	No	No	No

As nouns, snarl-up is a hypernym of gridlock; that is, snarl-up is a word with a broader meaning than gridlock:

gridlock: a traffic jam so bad that no movement is possible
snarl-up: a number of vehicles blocking one another until they can scarcely move

Other hypernyms of gridlock include traffic jam.

gridlock (noun)	snarl-up (noun)
a traffic jam so bad that no movement is possible	a number of vehicles blocking one another until they can scarcely move