The Collaborative International Dictionary of English v.0.48:

Alcove \Al"cove\ (?; 277), n. [F. alc[^o]ve, Sp. or Pg. alcoba,
   from Ar. al-quobbah arch, vault, tent.]
   1. (Arch.) A recessed portion of a room, or a small room
      opening into a larger one; especially, a recess to contain
      a bed; a lateral recess in a library.
      [1913 Webster]

   2. A small ornamental building with seats, or an arched seat,
      in a pleasure ground; a garden bower. --Cowper.
      [1913 Webster]

   3. Any natural recess analogous to an alcove or recess in an
      apartment.
      [1913 Webster]

            The youthful wanderers found a wild alcove.
                                                  --Falconer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

alcove
    n 1: a small recess opening off a larger room [syn: alcove,
         bay]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "alcove":
   arbor, bay, belvedere, bower, carrel, conservatory, corner, cove,
   cranny, cubby, cubbyhole, cubicle, gazebo, glasshouse, greenhouse,
   inglenook, kiosk, lathhouse, niche, nook, oriel, pagoda, pergola,
   pitchhole, recess, recession, retreat, roomlet, snuggery,
   summerhouse