swelling vs nubble

swelling and nubble both are nouns.

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

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

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

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

swelling (noun)	nubble (noun)
the increase in volume of certain substances when they are heated (often accompanied by release of water)	a small lump or protuberance
something that bulges out or is protuberant or projects from its surroundings
an abnormal protuberance or localized enlargement