The Collaborative International Dictionary of English v.0.48:

Bulb \Bulb\, v. i.
   To take the shape of a bulb; to swell.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bulb \Bulb\ (b[u^]lb), n. [L. bulbus, Gr. bolbo`s: cf. F.
   bulbe.]
   1. (Bot.) A spheroidal body growing from a plant either above
      or below the ground (usually below), which is strictly a
      bud, consisting of a cluster of partially developed
      leaves, and producing, as it grows, a stem above, and
      roots below, as in the onion, tulip, etc. It differs from
      a corm in not being solid.
      [1913 Webster]

   2. (Anat.) A name given to some parts that resemble in shape
      certain bulbous roots; as, the bulb of the aorta.
      [1913 Webster]

   Bulb of the eye, the eyeball.

   Bulb of a hair, the "root," or part whence the hair
      originates.

   Bulb of the spinal cord, the medulla oblongata, often
      called simply bulb.

   Bulb of a tooth, the vascular and nervous papilla contained
      in the cavity of the tooth.
      [1913 Webster]

   3. An expansion or protuberance on a stem or tube, as the
      bulb of a thermometer, which may be of any form, as
      spherical, cylindrical, curved, etc. --Tomlinson.
      [1913 Webster]

   3. a light bulb.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bulb
    n 1: a modified bud consisting of a thickened globular
         underground stem serving as a reproductive structure
    2: electric lamp consisting of a transparent or translucent
       glass housing containing a wire filament (usually tungsten)
       that emits light when heated by electricity [syn: light
       bulb, lightbulb, bulb, incandescent lamp, electric
       light, electric-light bulb]
    3: a rounded part of a cylindrical instrument (usually at one
       end); "the bulb of a syringe"
    4: anything with a round shape resembling a teardrop
    5: lower or hindmost part of the brain; continuous with spinal
       cord; (`bulb' is an old term for medulla oblongata); "the
       medulla oblongata is the most vital part of the brain because
       it contains centers controlling breathing and heart
       functioning" [syn: medulla oblongata, medulla, bulb]
    6: a rounded dilation or expansion in a canal or vessel or organ

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "bulb":
   ball, balloon, bilge, bladder, blain, bleb, blister, blob, boll,
   bolus, boss, bow, bubble, bulbil, bulblet, bulge, bulla, bump,
   bunch, burl, button, cahot, chine, clump, condyle, convex, corm,
   dowel, ear, ellipsoid, flange, flap, gall, geoid, globe, globelet,
   globoid, globule, glomerulus, gnarl, gob, gobbet, handle, hill,
   hump, hunch, jog, joggle, knob, knot, knur, knurl, lip, loop, lump,
   mole, mountain, nevus, nub, nubbin, nubble, oblate spheroid, orb,
   orbit, orblet, papilloma, peg, pellet, prolate spheroid, radicle,
   radix, rhizome, rib, ridge, ring, rondure, root, rootstock,
   shoulder, sphere, spheroid, spherule, spine, stud, style, tab, tap,
   taproot, tuber, tubercle, tubercule, verruca, vesicle, wale, wart,
   welt