start up vs kick-start

start up and kick-start both are verbs.

Word	Noun	Adjective	Verb	Adverb
start up	No	No	Yes	No
kick-start	No	No	Yes	No

As verbs, kick-start is a hyponym of start up; that is, kick-start is a word with a more specific, narrower meaning than start up:

Other hyponyms of start up include hot-wire, re-start, restart, crank, crank up, jump-start, jump, jumpstart.

start up (verb)	kick-start (verb)
get off the ground	start (a motorcycle) by means of a kick starter
get going or set in motion