The Collaborative International Dictionary of English v.0.48:

Diver \Div"er\, n.
   1. One who, or that which, dives.
      [1913 Webster]

            Divers and fishers for pearls.        --Woodward.
      [1913 Webster]

   2. Fig.: One who goes deeply into a subject, study, or
      business. "A diver into causes." --Sir H. Wotton.
      [1913 Webster]

   3. (Zool.) Any bird of certain genera, as Urinator
      (formerly Colymbus), or the allied genus Colymbus, or
      Podiceps, remarkable for their agility in diving.
      [1913 Webster]

   Note: The northern diver (Urinator imber) is the loon; the
         black diver or velvet scoter (Oidemia fusca) is a sea
         duck. See Loon, and Scoter.
         [1913 Webster]

WordNet (r) 3.0 (2006):

diver
    n 1: someone who works underwater [syn: diver, frogman,
         underwater diver]
    2: someone who dives (into water) [syn: diver, plunger]
    3: large somewhat primitive fish-eating diving bird of the
       northern hemisphere having webbed feet placed far back;
       related to the grebes [syn: loon, diver]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "diver":
   bather, bathing beauty, bathing girl, cannon, cutpurse,
   deep-sea diver, dip, free diver, frogman, jumper, mermaid, merman,
   natator, parachute jumper, pearl diver, plunger, scuba diver,
   skin diver, sky diver, snorkel diver, swimmer, wire