to hail a cab

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]