buy time vs delay

buy time is not a noun while delay is a noun.

Word	Noun	Adjective	Verb	Adverb
buy time	No	No	Yes	No
delay	Yes	No	Yes	No

As verbs, delay is a hypernym of buy time; that is, delay is a word with a broader meaning than buy time:

buy time: act so as to delay an event or action in order to gain an advantage
delay: cause to be slowed down or delayed

Other hypernyms of buy time include detain, hold up.

buy time (noun)	delay (noun)
	the act of delaying; inactivity resulting in something being put off until a later time
	time during which some action is awaited

buy time (verb)	delay (verb)
act so as to delay an event or action in order to gain an advantage	cause to be slowed down or delayed
	stop or halt
	slow the growth or development of
	act later than planned, scheduled, or required