strike up vs initiate

strike up is not a noun while initiate is a noun.

Word	Noun	Adjective	Verb	Adverb
strike up	No	No	Yes	No
initiate	Yes	No	Yes	No

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

Other hypernyms of strike up include pioneer.

strike up (noun)	initiate (noun)
	people who have been introduced to the mysteries of some field or activity
	someone who has been admitted to membership in a scholarly field
	someone new to a field or activity

strike up (verb)	initiate (verb)
begin	set in motion, start an event or prepare the way for
start playing	bring up a topic for discussion
	take the lead or initiative in; participate in the development of
	bring into being
	accept people into an exclusive society or group, usually with some rite