tunnel vs delve

tunnel is a noun but delve is not a noun.

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

As verbs, delve is a hypernym of tunnel; that is, delve is a word with a broader meaning than tunnel:

Other hypernyms of tunnel include cut into, dig, turn over.

tunnel (noun)	delve (noun)
a passageway through or under something, usually underground (especially one for trains or cars)
a hole made by an animal, usually for shelter

tunnel (verb)	delve (verb)
force a way through	turn up, loosen, or remove earth
move through by or as by digging