pocketknife vs penknife

pocketknife and penknife both are nouns.

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

As nouns, penknife is a hyponym of pocketknife; that is, penknife is a word with a more specific, narrower meaning than pocketknife:

pocketknife: a knife with a blade that folds into the handle; suitable for carrying in the pocket
penknife: a small pocketknife; originally used to cut quill pens

Other hyponyms of pocketknife include clasp knife, jackknife, flick-knife, flick knife, switchblade, switchblade knife.

pocketknife (noun)	penknife (noun)
a knife with a blade that folds into the handle; suitable for carrying in the pocket	a small pocketknife; originally used to cut quill pens