WordNet (r) 3.0 (2006):

tour de force
    n 1: a masterly or brilliant feat

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "tour de force":
   accomplished fact, accomplishment, achievement, act, acta, action,
   adventure, blow, classic, coup, dealings, deed, doing, doings,
   effort, endeavor, enterprise, exploit, fait accompli, feat, gest,
   go, hand, handiwork, job, magnum, maneuver, master stroke,
   masterpiece, masterwork, measure, move, operation, overt act,
   passage, performance, proceeding, production, res gestae, step,
   stroke, stunt, thing, thing done, transaction, turn, undertaking,
   work, works