WordNet (r) 3.0 (2006):

frogman
    n 1: someone who works underwater [syn: diver, frogman,
         underwater diver]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "frogman":
   Naval Reservist, Royal Marine, Seabee, bather, bathing beauty,
   bathing girl, bluejacket, boot, cadet, deep-sea diver, diver,
   free diver, gob, horse marine, jolly, jumper, marine, mermaid,
   merman, midshipman, midshipmite, natator, naval cadet, navy man,
   parachute jumper, pearl diver, plunger, scuba diver, skin diver,
   sky diver, snorkel diver, swabbie, swimmer