The Collaborative International Dictionary of English v.0.48:

Caveat \Ca"ve*at\, n. [L. caved let him beware, pres. subj. of
   cavere to be on one's guard to, beware.]
   [1913 Webster]
   1. (Law) A notice given by an interested party to some
      officer not to do a certain act until the party is heard
      in opposition; as, a caveat entered in a probate court to
      stop the proving of a will or the taking out of letters of
      administration, etc. --Bouvier.
      [1913 Webster]

   2. (U. S. Patent Laws) A description of some invention,
      designed to be patented, lodged in the patent office
      before the patent right is applied for, and operating as a
      bar to the issue of letters patent to any other person,
      respecting the same invention.
      [1913 Webster]

   Note: A caveat is operative for one year only, but may be
         renewed.
         [1913 Webster]

   3. Intimation of caution; warning; protest.
      [1913 Webster]

            We think it right to enter our caveat against a
            conclusion.                           --Jeffrey.
      [1913 Webster]

   Caveat emptor [L.] (Law), let the purchaser beware, i. e.,
      let him examine the article he is buying, and act on his
      own judgment.
      [1913 Webster]

WordNet (r) 3.0 (2006):

caveat
    n 1: a warning against certain acts; "a caveat against unfair
         practices" [syn: caution, caveat]
    2: (law) a formal notice filed with a court or officer to
       suspend a proceeding until filer is given a hearing; "a
       caveat filed against the probate of a will"