Source : Webster's Revised Unabridged Dictionary (1913)

Chiasmus \Chi*as"mus\, n. [NL., fr. Gr. ? a placing crosswise,
   fr. ?. See {Chiasm}.] (Rhet.)
   An inversion of the order of words or phrases, when repeated
   or subsequently referred to in a sentence; thus,

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

Source : WordNet®

chiasmus
     n : inversion in the second of two parallel phrases
     [also: {chiasmi} (pl)]