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):

taxicab
    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]