The Collaborative International Dictionary of English v.0.48:

Levorotatory \Le`vo*ro"ta*to*ry\ (-r[=o]"t[.a]*t[-o]*r[y^]), a.
   [Levo- + rotatory.] (Chem. & Physics)
   Turning or rotating the plane of polarization of light
   towards the left; -- applied to crystals and compounds
   exhibiting optical activity, such as levulose, left-handed
   quartz crystals, etc. Opposite of dextrorotatory. [Written
   also l[ae]vorotatory.]
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

levorotatory
    adj 1: rotating to the left [syn: levorotary, levorotatory,
           left-handed]