gridlock vs traffic jam

gridlock and traffic jam both are nouns.

Word	Noun	Adjective	Verb	Adverb
gridlock	Yes	No	No	No
traffic jam	Yes	No	No	No

As nouns, traffic jam is a hypernym of gridlock; that is, traffic jam is a word with a broader meaning than gridlock:

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

Other hypernyms of gridlock include snarl-up.

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