The Collaborative International Dictionary of English v.0.48:

Levorotation \Le`vo*ro*ta"tion\, n. [Written also
   l[ae]vorotation.] [Levo- + rotation.] (Physics & Chem.)
   Rotation in the direction of an outgoing right-handed screw;
   counter-clockwise rotation; -- applied chiefly to the turning
   of the plane of polarization of light.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

levorotation
    n 1: rotation to the left [syn: levorotation,
         counterclockwise rotation] [ant: clockwise rotation,
         dextrorotation]