dam vs obstruct

dam is a noun but obstruct is not a noun.

Word	Noun	Adjective	Verb	Adverb
dam	Yes	No	Yes	No
obstruct	No	No	Yes	No

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

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

dam (noun)	obstruct (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)	obstruct (verb)
obstruct with, or as if with, a dam	block passage through
	shut out from view or get in the way so as to hide from sight
	hinder or prevent the progress or accomplishment of