The Collaborative International Dictionary of English v.0.48:

Belfry \Bel"fry\, n. [OE. berfray movable tower used in sieges,
   OF. berfreit, berfroit, F. beffroi, fr. MHG. bervrit,
   bercvrit, G. bergfriede, fr. MHG. bergen to protect (G.
   bergen to conceal) + vride peace, protection, G. friede
   peace; in compounds often taken in the sense of security, or
   place of security; orig. therefore a place affording
   security. G. friede is akin to E. free. See Burg, and
   Free.]
   1. (Mil. Antiq.) A movable tower erected by besiegers for
      purposes of attack and defense.
      [1913 Webster]

   2. A bell tower, usually attached to a church or other
      building, but sometimes separate; a campanile.
      [1913 Webster]

   3. A room in a tower in which a bell is or may be hung; or a
      cupola or turret for the same purpose.
      [1913 Webster]

   4. (Naut.) The framing on which a bell is suspended.
      [1913 Webster]

WordNet (r) 3.0 (2006):

belfry
    n 1: a bell tower; usually stands alone unattached to a building
         [syn: campanile, belfry]
    2: a room (often at the top of a tower) where bells are hung