NOUN (1)

1. a swimming stroke that resembles the crawl except the swimmer lies on his or her back;


VERB (1)

1. swim on one's back;

The Collaborative International Dictionary of English v.0.48:

backstroke \back"stroke`\ n.
   1. a swimming stroke that resembles the crawl except the
      swimmer lies on his or her back. It is usually executed
      with backward-moving circular arm strokes and a flutter
      kick.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

backstroke
    n 1: a swimming stroke that resembles the crawl except the
         swimmer lies on his or her back
    v 1: swim on one's back

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "backstroke":
   Australian crawl, Long Melford, aquaplaning, aquatics, backhand,
   backhander, balneation, bathe, bathing, bolo punch, breaststroke,
   butterfly, crawl, diving, dog paddle, fin, fishtail, flapper,
   flipper, floating, haymaker, hook, natation, one-two,
   round-arm blow, roundhouse, short-arm blow, sidestroke, sidewinder,
   surfboarding, surfing, swim, swimming, swing, treading water,
   uppercut, wading, waterskiing