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]