initiate vs spark off

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

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

As verbs, spark off is a hyponym of initiate; that is, spark off is a word with a more specific, narrower meaning than initiate:

initiate (noun)	spark off (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

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