The Collaborative International Dictionary of English v.0.48:

Monoclinic \Mon`o*clin"ic\, a. [Mono- + Gr. ? to incline.]
   (Crystallog.)
   Having one oblique intersection; -- said of that system of
   crystallization in which the vertical axis is inclined to
   one, but at right angles to the other, lateral axis. See
   Crystallization.
   [1913 Webster]

WordNet (r) 3.0 (2006):

monoclinic
    adj 1: having three unequal crystal axes with one oblique
           intersection; "monoclinic system" [ant: anorthic,
           triclinic]