snarl-up vs gridlock

snarl-up and gridlock both are nouns.

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

As nouns, gridlock is a hyponym of snarl-up; that is, gridlock is a word with a more specific, narrower meaning than snarl-up:

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

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