flick knife vs pocketknife

flick knife and pocketknife both are nouns.

Word	Noun	Adjective	Verb	Adverb
flick knife	Yes	No	No	No
pocketknife	Yes	No	No	No

As nouns, pocketknife is a hypernym of flick knife; that is, pocketknife is a word with a broader meaning than flick knife:

flick knife: a pocketknife with a blade that springs open at the press of a button
pocketknife: a knife with a blade that folds into the handle; suitable for carrying in the pocket

Other hypernyms of flick knife include pocket knife.

flick knife (noun)	pocketknife (noun)
a pocketknife with a blade that springs open at the press of a button	a knife with a blade that folds into the handle; suitable for carrying in the pocket