The Collaborative International Dictionary of English v.0.48:

taxi \tax"i\, n.
   1. same as taxicab.
      [PJC]

   2. any vehicle that carries passengers for a fare, as a water
      taxi.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

taxicab \tax"i*cab\, n.
   an automobile with a professional driver which can be hired
   to carry passengers; -- also called a taxi, and informally
   called a cab or a hack. The driver of a taxicab is
   referred to as a cab driver or cabbie, and sometimes as a
   chauffeur or hackie.

   Note: Taxicabs may be engaged by a prior appointment made,
         e.g. by telephone, or they may cruise for passengers,
         i.e. they may drive in city streets and stop to pick up
         pasengers when they are signalled by a prospective
         passenger. The act of signalling a taxicab (usually by
         a wave of the arm) is often called

   to hail a cab or

   to flag down a cab.
      [PJC]

WordNet (r) 3.0 (2006):

taxi
    n 1: a car driven by a person whose job is to take passengers
         where they want to go in exchange for money [syn: cab,
         hack, taxi, taxicab]
    v 1: travel slowly; "The plane taxied down the runway"
    2: ride in a taxicab [syn: taxi, cab]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "taxi":
   autobus, become airborne, bicycle, bike, bus, cab, catch a train,
   chartered bus, chauffeur, clear, cycle, diligence, double-decker,
   drive, entrain, fly aloft, go by rail, hack, hackney, hired car,
   jitney, joyride, jump off, leave the ground, mail coach,
   make a train, motor, motor coach, motorbus, motorcycle, omnibus,
   pedal, post coach, ride, rotate, stage, stagecoach, take a joyride,
   take off, taxicab, wheel