spark off vs initiate

spark off is not a noun while initiate is a noun.

Word	Noun	Adjective	Verb	Adverb
spark off	No	No	Yes	No
initiate	Yes	No	Yes	No

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

Other hypernyms of spark off include pioneer.

spark off (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

spark off (verb)	initiate (verb)
put in motion or move to act	set in motion, start an event or prepare the way for
	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