"stunted ear of corn," 1690s, American English colloquial diminutive of nub. General sense of "small piece" is from 1857.
Entries linking to nubbin
nub n.
"knob, lump, bump, protuberance," 1590s, variant of dialectal knub, which is probably a variant of knob. Figurative meaning "point, gist" is attested by 1834.