The Collaborative International Dictionary of English v.0.48:

Sinistral \Sin"is*tral\, a.
   1. Of or pertaining to the left, inclining to the left;
      sinistrous; -- opposed to dextral.
      [1913 Webster]

   2. (Zool.) Having the whorls of the spire revolving or rising
      to the left; reversed; -- said of certain spiral shells.
      [1913 Webster]

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):

sinistral
    adj 1: of or on the left; "a sinistral gastropod shell with the
           apex upward has its opening on the left when facing the
           observer"; "a sinistral flatfish lies with the left eye
           uppermost" [ant: dextral]
    2: preferring to use left foot or hand or eye; "sinistral
       individuals exhibit dominance of the left hand and eye"