The Collaborative International Dictionary of English v.0.48:

Groom \Groom\, n. [Cf. Scot. grome, groyme, grume, gome, guym,
   man, lover, OD. grom boy, youth; perh. the r is an insertion
   as in E. bridegroom, and the word is the same as AS. guma
   man. See Bridegroom.]
   1. A boy or young man; a waiter; a servant; especially, a man
      or boy who has charge of horses, or the stable. --Spenser.
      [1913 Webster]

   2. One of several officers of the English royal household,
      chiefly in the lord chamberlain's department; as, the
      groom of the chamber; the groom of the stole.
      [1913 Webster]

   3. A man recently married, or about to be married; a
      bridegroom. --Dryden.
      [1913 Webster]

   Groom porter, formerly an officer in the English royal
      household, who attended to the furnishing of the king's
      lodgings and had certain privileges.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Groom \Groom\, v. i. [imp. & p. p. Groomed; p. pr. & vb. n.
   Grooming.]
   To tend or care for, or to curry or clean, as a, horse.
   [1913 Webster]

WordNet (r) 3.0 (2006):

groom
    n 1: a man participant in his own marriage ceremony [syn:
         groom, bridegroom]
    2: someone employed in a stable to take care of the horses [syn:
       stableman, stableboy, groom, hostler, ostler]
    3: a man who has recently been married [syn: groom,
       bridegroom]
    v 1: educate for a future role or function; "He is grooming his
         son to become his successor"; "The prince was prepared to
         become King one day"; "They trained him to be a warrior"
         [syn: prepare, groom, train]
    2: give a neat appearance to; "groom the dogs"; "dress the
       horses" [syn: dress, groom, curry]
    3: care for one's external appearance; "He is always well-
       groomed" [syn: groom, neaten]