nub vs nubbin

nub and nubbin both are nouns.

Word	Noun	Adjective	Verb	Adverb
nub	Yes	No	No	No
nubbin	Yes	No	No	No

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

nub (noun)	nubbin (noun)
the choicest or most essential or most vital part of some idea or experience	a small nub (especially an undeveloped fruit or ear of corn)
a small piece
a small lump or protuberance