The Collaborative International Dictionary of English v.0.48:

Grave \Grave\, a. [Compar. Graver (gr[=a]v"[~e]r); superl.
   Gravest.] [F., fr. L. gravis heavy; cf. It. & Sp. grave
   heavy, grave. See Grief.]
   1. Of great weight; heavy; ponderous. [Obs.]
      [1913 Webster]

            His shield grave and great.           --Chapman.
      [1913 Webster]

   2. Of importance; momentous; weighty; influential; sedate;
      serious; -- said of character, relations, etc.; as, grave
      deportment, character, influence, etc.
      [1913 Webster]

            Most potent, grave, and reverend seigniors. --Shak.
      [1913 Webster]

            A grave and prudent law, full of moral equity.
                                                  --Milton.
      [1913 Webster]

   3. Not light or gay; solemn; sober; plain; as, a grave color;
      a grave face.
      [1913 Webster]

   4. (Mus.)
      (a) Not acute or sharp; low; deep; -- said of sound; as, a
          grave note or key.
          [1913 Webster]

                The thicker the cord or string, the more grave
                is the note or tone.              --Moore
                                                  (Encyc. of
                                                  Music).
      (b) Slow and solemn in movement.
          [1913 Webster]

   Grave accent. (Pron.) See the Note under Accent, n., 2.

   Syn: Solemn; sober; serious; sage; staid; demure; thoughtful;
        sedate; weighty; momentous; important.

   Usage: Grave, Sober, Serious, Solemn. Sober supposes
          the absence of all exhilaration of spirits, and is
          opposed to gay or flighty; as, sober thought. Serious
          implies considerateness or reflection, and is opposed
          to jocose or sportive; as, serious and important
          concerns. Grave denotes a state of mind, appearance,
          etc., which results from the pressure of weighty
          interests, and is opposed to hilarity of feeling or
          vivacity of manner; as, a qrave remark; qrave attire.
          Solemn is applied to a case in which gravity is
          carried to its highest point; as, a solemn admonition;
          a solemn promise.
          [1913 Webster]

WordNet (r) 3.0 (2006):

grave accent
    n 1: a mark (`) placed above a vowel to indicate pronunciation
         [syn: grave accent, grave]