The Collaborative International Dictionary of English v.0.48:

counterclockwise \coun"ter*clock"wise\ adj. & adv.
   in the opposite direction to that in which the hands of a
   clock rotate, as viewed from in front of the clock face; --
   of rotatory motion or spiral direction. Opposite of
   clockwise, or right-handed

   Note: [Narrower terms: sinistral levororotary,
         levorotatory]

   Syn: left-handed.
        [PJC]

WordNet (r) 3.0 (2006):

counterclockwise
    adv 1: in a direction opposite to the direction in which the
           hands of a clock move; "please move counterclockwise in a
           circle!" [syn: counterclockwise, anticlockwise] [ant:
           clockwise]
    adj 1: in the direction opposite to the rotation of the hands of
           a clock [syn: counterclockwise, anticlockwise,
           contraclockwise] [ant: clockwise]