The Collaborative International Dictionary of English v.0.48:

Protuberance \Pro*tu"ber*ance\, n. [Cf. F. protub['e]rance. See
   Protuberant.]
   That which is protuberant swelled or pushed beyond the
   surrounding or adjacent surface; a swelling or tumor on the
   body; a prominence; a bunch or knob; an elevation.
   [1913 Webster]

   Solar protuberances (Astron.), certain rose-colored masses
      on the limb of the sun which are seen to extend beyond the
      edge of the moon at the time of a solar eclipse. They may
      be discovered with the spectroscope on any clear day.
      Called also solar prominences. See Illust. in Append.
      [1913 Webster]

   Syn: Projection, Protuberance. protuberance differs from
        projection, being applied to parts that rise from the
        surface with a gradual ascent or small angle; whereas a
        projection may be at a right angle with the surface.
        [1913 Webster]

WordNet (r) 3.0 (2006):

protuberance
    n 1: something that bulges out or is protuberant or projects
         from its surroundings; "the gun in his pocket made an
         obvious bulge"; "the hump of a camel"; "he stood on the
         rocky prominence"; "the occipital protuberance was well
         developed"; "the bony excrescence between its horns" [syn:
         bulge, bump, hump, swelling, gibbosity,
         gibbousness, jut, prominence, protuberance,
         protrusion, extrusion, excrescence]
    2: the condition of being protuberant; the condition of bulging
       out; "the protuberance of his belly"

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "protuberance":
   bas-relief, bellying, boldness, bulge, bulging, embossment,
   eminence, excrescence, excrescency, extrusion, feel, finish,
   gibbosity, gibbousness, grain, granular texture, high relief,
   indentation, jut, knub, low relief, nap, nub, pile, pit, pock,
   projection, prominence, protrusion, protuberancy, relief, salience,
   salient, shag, structure, surface, surface texture, texture,
   tuberosity, tuberousness, wale, weave, woof