The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "specialist":
   Wall Streeter, adept, aficionado, amateur, anesthesiologist,
   artist, artiste, authoritative, authority, bond crowd, broker,
   buff, cardiologist, chiropodist, confined, connoisseur, critic,
   curb broker, dealer, dermatologist, dilettante, expert, eye doctor,
   eye-ear-nose-throat specialist, fan, feature, featured,
   floor broker, floor trader, floorman, freak, geriatrician,
   gerontologist, gynecologist, immunologist, internist, jobber,
   knowledgeable, limited, maestro, master, neurologist, nut,
   obstetrician, oculist, odd-lot dealer, ophthalmologist,
   orthopedist, otolaryngologist, otologist, pathologist,
   pediatrician, pediatrist, pit man, podiatrist, professional,
   psychiatrist, pundit, radiologist, registered representative,
   restricted, savant, scholar, serologist, sharebroker, skin man,
   specialistic, specialized, stock dealer, stock-exchange broker,
   stockbroker, stockjobber, technical, technical expert, technician,
   two-dollar broker