Source : Webster's Revised Unabridged Dictionary (1913)

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.

   {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.

   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.

Source : WordNet®

protuberance
     n 1: something that bulges out or is protuberant or projects from
          a form [syn: {bulge}, {bump}, {hump}, {gibbosity}, {gibbousness},
           {jut}, {prominence}, {protrusion}, {extrusion}, {excrescence}]
     2: the condition of being protuberant; the condition of bulging
        out; "the protuberance of his belly"