Source : Webster's Revised Unabridged Dictionary (1913)

Specialist \Spe"cial*ist\, n.
   One who devotes himself to some specialty; as, a medical
   specialist, one who devotes himself to diseases of particular
   parts of the body, as the eye, the ear, the nerves, etc.

Source : WordNet®

specialist
     n 1: an expert who is devoted to one occupation or branch of
          learning [syn: {specializer}, {specialiser}] [ant: {Renaissance
          man}]
     2: practices one branch of medicine [syn: {medical specialist}]