The Collaborative International Dictionary of English v.0.48:

Yacht \Yacht\ (y[o^]t), n. [D. jagt, jacht; perhaps properly, a
   chase, hunting, from. jagen to chase, hunt, akin to G. jagen,
   OHG. jag[=o]n, of uncertain origin; or perhaps akin to OHG.
   g[=a]hi quick, sudden (cf. Gay).] (Naut.)
   A light and elegantly furnished vessel, used either for
   private parties of pleasure, or as a vessel of state to
   convey distinguished persons from one place to another; a
   seagoing vessel used only for pleasure trips, racing, etc.
   [1913 Webster]

   Yacht measurement. See the Note under Tonnage, 4.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Yacht \Yacht\, v. i.
   To manage a yacht; to voyage in a yacht.
   [1913 Webster]

WordNet (r) 3.0 (2006):

yacht
    n 1: an expensive vessel propelled by sail or power and used for
         cruising or racing [syn: yacht, racing yacht]
    v 1: travel in a yacht

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "yacht":
   bark, bawley, bilander, boat, brig, brigantine, bully, buss, canoe,
   caravel, carry sail, cat, catamaran, circumnavigate, clipper,
   coast, corsair, corvette, cross, cruise, cutter, dandy, dhow,
   dromond, fishing smack, flattie, four-masted bark, four-master,
   frigate, galiot, galleass, galleon, go by ship, go on shipboard,
   go to sea, hooker, hoy, ice yacht, junk, keelboat, ketch,
   knockabout, lateen, lateener, lorcha, lugger, make a passage,
   motorboat, navigate, nobby, ocean racer, outrigger, pilot boat,
   pinnace, piragua, pirogue, ply, pram, pungy, racing yacht, rigger,
   row, run, sail, sail round, sail the sea, sailing auxiliary,
   sailing canoe, sailing dinghy, sailing packet, sailing trawler,
   sampan, sandbagger, schooner, scooter, scull, seafare, shallop,
   sharpie, shipentine, skipjack, sloop, smack, smack boat, snow,
   steam, steamboat, take a voyage, tartan, topsail schooner,
   traverse, trimaran, voyage, well smack, whaler, wool-clipper,
   xebec, yawl