dam vs close up

dam is a noun but close up is not a noun.

Word	Noun	Adjective	Verb	Adverb
dam	Yes	No	Yes	No
close up	No	No	Yes	Yes

As verbs, close up is a hypernym of dam; that is, close up is a word with a broader meaning than dam:

Other hypernyms of dam include block, impede, jam, obstruct, obturate, occlude.

dam (noun)	close up (noun)
female parent of an animal especially domestic livestock
a barrier constructed to contain the flow of water or to keep out the sea
a metric unit of length equal to ten meters

dam (verb)	close up (verb)
obstruct with, or as if with, a dam	refuse to talk or stop talking; fall silent
	block passage through
	unite or bring into contact or bring together the edges of
	cease to operate or cause to cease operating

dam (adverb)	close up (adverb)
	very close