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]