Source : Webster's Revised Unabridged Dictionary (1913)

Bell pepper \Bell" pep`per\ (Bot.)
   A species of Capsicum, or Guinea pepper ({C. annuum}). It is
   the red pepper of the gardens.

Source : WordNet®

bell pepper
     n 1: plant bearing large mild thick-walled usually bell-shaped
          fruits; the principal salad peppers [syn: {sweet pepper},
           {pimento}, {pimiento}, {paprika}, {sweet pepper plant},
           {Capsicum annuum grossum}]
     2: large bell-shaped sweet pepper in green or red or yellow or
        orange or black varieties