The Collaborative International Dictionary of English v.0.48:

Difform \Dif"form`\, a. [Cf. F. difforme, fr. L. dif- = dis- +
   forma form. Cf. Deform.]
   Irregular in form; -- opposed to uniform; anomalous; hence,
   unlike; dissimilar; as, to difform corolla, the parts of
   which do not correspond in size or proportion; difform
   leaves.
   [1913 Webster]

         The unequal refractions of difform rays. --Sir I.
                                                  Newton.
   [1913 Webster]