The Collaborative International Dictionary of English v.0.48:

sign language \sign" lang`uage\ (s[imac]n" l[a^]ng`w[asl]j), n.
   A form of language for communicating by use of gestures made
   by the hands, rather than by speech. It includes alphabets
   made by hand gestures, as well as proper languages formed
   from signs. Among the latter is the American Sign Language
   (ASL), used by the deaf. See also dactylology.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

American sign language \American sign language\ n.
   a sign language, used in the United States mostly by the deaf
   or for communication with the deaf, in which gestures made
   with the hands symbolize words, alphabetical letters, or
   ideas, permitting rapid communication in the absence of
   speech.

   Syn: Ameslan.
        [PJC]

WordNet (r) 3.0 (2006):

American sign language
    n 1: the sign language used in the United States [syn: ASL,
         American sign language]