Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

levorotation
     n : rotation to the left [syn: {counterclockwise rotation}]
         [ant: {dextrorotation}]