The Collaborative International Dictionary of English v.0.48:

Horticulture \Hor"ti*cul`ture\, n. [L. hortus garden + cultura
   culture: cf. F. horticulture. See Yard an inclosure, and
   Culture.]
   The cultivation of a garden or orchard; the art of
   cultivating gardens or orchards.
   [1913 Webster]

WordNet (r) 3.0 (2006):

horticulture
    n 1: the cultivation of plants [syn: gardening,
         horticulture]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "horticulture":
   bloom, blossom, blow, citriculture, floret, floriculture, floscule,
   flower, flower gardening, flower-growing, floweret, fruit-growing,
   gardening, groundskeeping, hortorium, landscape architecture,
   landscape gardening, market gardening, olericulture, orcharding,
   pomiculture, posy, truck gardening, viniculture, wildflower