The Collaborative International Dictionary of English v.0.48:
Protuberance \Pro*tu"ber*ance\, n. [Cf. F. protub['e]rance. See
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.