The Collaborative International Dictionary of English v.0.48:

Syndrome \Syn"dro*me\, n. [NL., from Gr. ?; sy`n with + ? a
   course, a running.]
   1. Concurrence. [R.] --Glanvill.
      [1913 Webster]

   2. (Med.) A group of symptoms occurring together that are
      characteristic and indicative of some underlying cause,
      such as a disease.
      [1913 Webster]

   3. generally, a pattern of characteristics or behaviors
      occurring together, that are sufficiently common and
      distinctive to indicate that they are due to a known
      cause.
      [PJC]

WordNet (r) 3.0 (2006):

syndrome
    n 1: a complex of concurrent things; "every word has a syndrome
         of meanings"
    2: a pattern of symptoms indicative of some disease