protrusion vs nubble

protrusion and nubble both are nouns.

Word	Noun	Adjective	Verb	Adverb
protrusion	Yes	No	No	No
nubble	Yes	No	No	No

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

protrusion: something that bulges out or is protuberant or projects from its surroundings
nubble: a small lump or protuberance

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

protrusion (noun)	nubble (noun)
the act of projecting out from something	a small lump or protuberance
something that bulges out or is protuberant or projects from its surroundings