The Collaborative International Dictionary of English v.0.48:

Res \Res\ (r?z), n.; pl. Res. [L.]
   A thing; the particular thing; a matter; a point.
   [1913 Webster]

   Res gestae [L., things done] (Law), the facts which form
      the environment of a litigated issue. --Wharton.

   Res judicata [L.] (Law), a thing adjudicated; a matter no
      longer open to controversy.
      [1913 Webster]

WordNet (r) 3.0 (2006):

res judicata
    n 1: a matter already settled in court; cannot be raised again
         [syn: res judicata, res adjudicata]