dam up vs jam

dam up is not a noun while jam is a noun.

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

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

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

dam up (noun)	jam (noun)
	deliberate radiation or reflection of electromagnetic energy for the purpose of disrupting enemy use of electronic devices or systems
	preserve of crushed fruit
	a dense crowd of people
	informal terms for a difficult situation

dam up (verb)	jam (verb)
obstruct with, or as if with, a dam	interfere with or prevent the reception of signals
	crowd or pack to capacity
	get stuck and immobilized
	block passage through
	crush or bruise
	press tightly together or cram
	push down forcibly