jackknife vs pocketknife

jackknife and pocketknife both are nouns.

Word	Noun	Adjective	Verb	Adverb
jackknife	Yes	No	Yes	No
pocketknife	Yes	No	No	No

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

jackknife: a large knife with one or more folding blades
pocketknife: a knife with a blade that folds into the handle; suitable for carrying in the pocket

Other hypernyms of jackknife include pocket knife.

jackknife (noun)	pocketknife (noun)
a dive in which the diver bends to touch the ankles before straightening out	a knife with a blade that folds into the handle; suitable for carrying in the pocket
a large knife with one or more folding blades

jackknife (verb)	pocketknife (verb)
dive into the water bending the body at the waist at a right angle, like a jackknife