The Collaborative International Dictionary of English v.0.48:

aspartame \aspartame\ n.
   1. an artificial sweetener containing an aspartic acid
      peptide, (C14H18N2O5); it is 160 times sweeter than
      sucrose (cane sugar) and is used as a calorie-free
      sweetener. Chemically it is
      N-L-[alpha]-aspartyl-L-phenylalanine-1-methyl ester. It is
      sold also under the trade name Equal.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

aspartame
    n 1: an artificial sweetener made from aspartic acid; used as a
         calorie-free sweetener