underline vs punctuate

underline is a noun but punctuate is not a noun.

Word	Noun	Adjective	Verb	Adverb
underline	Yes	No	Yes	No
punctuate	No	No	Yes	No

As verbs, punctuate is a hypernym of underline; that is, punctuate is a word with a broader meaning than underline:

Other hypernyms of underline include accent, accentuate, emphasise, emphasize, stress.

underline (noun)	punctuate (noun)
a line drawn underneath (especially under written matter)

underline (verb)	punctuate (verb)
give extra weight to (a communication)	insert punctuation marks into
draw a line or lines underneath to call attention to	interrupt periodically
	to stress, single out as important