The Collaborative International Dictionary of English v.0.48:

Bidet \Bi*det"\, n. [F. bidet, perh. fr. Celtic; cr. Gael.
   bideach very little, diminutive, bidein a diminutive animal,
   W. bidan a weakly or sorry wretch.]
   [1913 Webster]
   1. A small horse formerly allowed to each trooper or dragoon
      for carrying his baggage. --B. Jonson.
      [1913 Webster]

   2. A kind of bath tub for sitting baths; a sitz bath.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bidet
    n 1: a basin for washing genitals and anal area

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "bidet":
   aquamanile, automatic dishwasher, basin, bath, bathtub,
   carriage horse, cart horse, cavalry horse, dishpan, dishwasher,
   draft horse, dray horse, driving horse, ewer, fill horse, filler,
   finger bowl, gigster, hack, hackney, hunter, jument, kitchen sink,
   lavabo, lavatory, lead, leader, mount, pack horse, palfrey,
   piscina, plow horse, pole horse, polo pony, post-horse, remount,
   rider, riding horse, road horse, roadster, rouncy, saddle horse,
   saddler, shaft horse, shower, shower bath, shower curtain,
   shower head, shower room, shower stall, showers, sink,
   stalking-horse, sumpter, sumpter horse, thill horse, thiller, tub,
   wash barrel, wash boiler, washbasin, washbowl, washdish, washer,
   washing machine, washing pot, washpot, washstand, washtub, wheeler,
   wheelhorse, workhorse