underpass vs tunnel

underpass and tunnel both are nouns.

Word	Noun	Adjective	Verb	Adverb
underpass	Yes	No	No	No
tunnel	Yes	No	Yes	No

As nouns, tunnel is a hypernym of underpass; that is, tunnel is a word with a broader meaning than underpass:

underpass: an underground tunnel or passage enabling pedestrians to cross a road or railway
tunnel: a passageway through or under something, usually underground (especially one for trains or cars)

underpass (noun)	tunnel (noun)
an underground tunnel or passage enabling pedestrians to cross a road or railway	a passageway through or under something, usually underground (especially one for trains or cars)
	a hole made by an animal, usually for shelter

underpass (verb)	tunnel (verb)
	force a way through
	move through by or as by digging