The Collaborative International Dictionary of English v.0.48:

Chiasmus \Chi*as"mus\ (k[-i]*[a^]z"m[u^]s), n. [NL., fr. Gr.
   chiasmo`s a placing crosswise, fr. chia`zein. See Chiasm.]
   (Rhet.)
   An inversion of the order of words or phrases, when repeated
   or subsequently referred to in a sentence; thus,
   [1913 Webster]

         If e'er to bless thy sons
         My voice or hands deny,
         These hands let useful skill forsake,
         This voice in silence die.               --Dwight.
   [1913 Webster]

WordNet (r) 3.0 (2006):

chiasmus
    n 1: inversion in the second of two parallel phrases