bulb

Short definition from Wiktionary

Noun

1. 1
   The bulb-shaped underground portion of a plant such as a tulip, consisting of a shortened stem and many fleshy scale leaves, from which the rest of the plant may be regrown.
2. 2
   The medulla oblongata.
3. 3
   Any solid object rounded at one end and tapering on the other, possibly attached to a larger object at the tapered end.
4. 4
   Any solid object rounded at one end and tapering on the other, possibly attached to a larger object at the tapered end: A light bulb (not necessarily bulbous in shape).
5. 5
   A bulbous protuberance at the forefoot of certain vessels to reduce turbulence.
6. 6
   An onion.

Verb

1. 1
   To take the shape of a bulb; to swell.