protuberance vs caput

protuberance and caput both are nouns.

Word	Noun	Adjective	Verb	Adverb
protuberance	Yes	No	No	No
caput	Yes	No	No	No

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

protuberance: something that bulges out or is protuberant or projects from its surroundings
caput: a headlike protuberance on an organ or structure

Other hyponyms of protuberance include frontal eminence, occipital protuberance, belly, mogul, nub, nubble, snag, wart.

protuberance (noun)	caput (noun)
something that bulges out or is protuberant or projects from its surroundings	the upper part of the human body or the front part of the body in animals; contains the face and brains
the condition of being protuberant; the condition of bulging out	a headlike protuberance on an organ or structure