The Collaborative International Dictionary of English v.0.48:

Garrison \Gar"ri*son\, v. t. [imp. & p. p. Garrisoned; p. pr.
   & vb. n. Garrisoning.] (Mil.)
   (a) To place troops in, as a fortification, for its defense;
       to furnish with soldiers; as, to garrison a fort or town.
   (b) To secure or defend by fortresses manned with troops; as,
       to garrison a conquered territory.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Garrison \Gar"ri*son\, n. [OE. garnisoun, F. garnison garrison,
   in OF. & OE. also, provision, munitions, from garnir to
   garnish. See Garnish.] (Mil.)
   (a) A body of troops stationed in a fort or fortified town.
   (b) A fortified place, in which troops are quartered for its
       security.
       [1913 Webster]

   In garrison, in the condition of a garrison; doing duty in
      a fort or as one of a garrison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

garrison
    n 1: a fortified military post where troops are stationed [syn:
         garrison, fort]
    2: United States abolitionist who published an anti-slavery
       journal (1805-1879) [syn: Garrison, William Lloyd
       Garrison]
    3: the troops who maintain and guard a fortified place
    v 1: station (troops) in a fort or garrison