doorknob vs knob

doorknob and knob both are nouns.

Word	Noun	Adjective	Verb	Adverb
doorknob	Yes	No	No	No
knob	Yes	No	No	No

As nouns, knob is a hypernym of doorknob; that is, knob is a word with a broader meaning than doorknob:

doorknob: a knob used to release the catch when opening a door (often called `doorhandle' in Great Britain)
knob: a round handle

doorknob (noun)	knob (noun)
a knob used to release the catch when opening a door (often called `doorhandle' in Great Britain)	a round handle
	a circular rounded projection or protuberance
	an ornament in the shape of a ball on the hilt of a sword or dagger
	any thickened enlargement