The Collaborative International Dictionary of English v.0.48:

Syllepsis \Syl*lep"sis\, n. [L., fr. Gr. sy`llhpsis a taking
   together, from ?. See syllable, n.]
   1. (Rhet.) A figure of speech by which a word is used in a
      literal and metaphorical sense at the same time.
      [1913 Webster]

   2. (Gram.) The agreement of a verb or adjective with one,
      rather than another, of two nouns, with either of which it
      might agree in gender, number, etc.; as, rex et regina
      beati.
      [1913 Webster] Sylleptic

WordNet (r) 3.0 (2006):

syllepsis
    n 1: use of a word to govern two or more words though agreeing
         in number or case etc. with only one