The Collaborative International Dictionary of English v.0.48:

Garret \Gar"ret\, n. [OE. garite, garette, watchtower, place of
   lookout, OF. garite, also meaning, a place of refuge, F.
   gu['e]rite a place of refuge, donjon, sentinel box, fr. OF.
   garir to preserve, save, defend, F. gu['e]rir to cure; of
   German origin; cf. OHG. werian to protect, defend, hinder, G.
   wehren, akin to Goth. warjan to hinder, and akin to E. weir,
   or perhaps to wary. See Weir, and cf. Guerite.]
   1. A turret; a watchtower. [Obs.]
      [1913 Webster]

            He saw men go up and down on the garrets of the
            gates and walls.                      --Ld. Berners.
      [1913 Webster]

   2. That part of a house which is on the upper floor,
      immediately under or within the roof; an attic.
      [1913 Webster]

            The tottering garrets which overhung the streets of
            Rome.                                 --Macaulay.
      [1913 Webster]

WordNet (r) 3.0 (2006):

garret
    n 1: floor consisting of open space at the top of a house just
         below roof; often used for storage [syn: loft, attic,
         garret]