tuber

noun

1. a short, thickened, fleshy part of an underground stem, as a potato: new plants develop from the buds, or eyes, that grow in the axils of the minute scale leaves of a tuber
2. Anat. a tubercle or swelling

Origin: L, lit., a swelling, knob, truffle < IE *teubh- < base *tēu-, to swell > thumb, L tumere, to swell