The Collaborative International Dictionary of English v.0.48:

astronaut \as"tro*naut\ adj.
   a person trained to travel in a spacecraft; one who travels
   in a spacecraft; -- called in the Soviet Union and Russia
   cosmonaut.

   Syn: spaceman, cosmonaut
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

astronaut
    n 1: a person trained to travel in a spacecraft; "the Russians
         called their astronauts cosmonauts" [syn: astronaut,
         spaceman, cosmonaut]

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "astronaut":
   Martian, adventurer, aeronaut, aeroplaner, aeroplanist, air pilot,
   airplanist, alien, alpinist, aviator, barnstormer, birdman, camper,
   captain, climber, cloud seeder, comers and goers, commercial pilot,
   commuter, copilot, cosmonaut, cosmopolite, crop-duster, cruiser,
   excursionist, explorer, fare, flier, globe-girdler, globe-trotter,
   goer, hajji, instructor, jet jockey, jet set, jet-setter,
   journeyer, licensed pilot, man from Mars, mariner, mountaineer,
   palmer, passenger, passerby, pathfinder, pilgrim, pilot, pioneer,
   planetary colony, rainmaker, rocket man, rocketeer, rubberneck,
   rubbernecker, sailor, sightseer, space crew, space traveler,
   spaceman, straphanger, stunt flier, stunt man, test pilot, tourer,
   tourist, trailblazer, trailbreaker, transient, traveler, trekker,
   tripper, viator, visiting fireman, voortrekker, voyager, voyageur,
   wayfarer, wingman, world-traveler