The Collaborative International Dictionary of English v.0.48:

Topiary \Top"i*a*ry\, a. [L. topiarius belonging to ornamental
   gardening, fr. topia (sc. opera) ornamental gardening, fr.
   Gr. ? a place.]
   Of or pertaining to ornamental gardening; produced by
   cutting, trimming, etc.; topiarian.
   [1913 Webster]

   Topiary work, arbors, shrubbery, hedges, or the like, cut
      and trimmed into fanciful forms, as of animals, buildings,
      etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

topiary
    n 1: a garden having shrubs clipped or trimmed into decorative
         shapes especially of animals
    2: making decorative shapes by trimming shrubs or trees