The Collaborative International Dictionary of English v.0.48:

Gid \Gid\, n. [Cf. Giddy, a.]
   A disease of sheep, characterized by vertigo; the staggers.
   It is caused by the presence of the C?nurus, a larval
   tapeworm, in the brain. See C?nurus.
   [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006):

GID
       Group ID