The Collaborative International Dictionary of English v.0.48:

Decorator \Dec"o*ra`tor\ (d[e^]k"[-o]*r[=a]"t[~e]r), n. [Cf. F.
   d['e]corateur.]
   One who decorates, adorns, or embellishes; specifically, an
   artisan whose business is the decoration of houses, esp.
   their interior decoration.
   [1913 Webster]

WordNet (r) 3.0 (2006):

decorator
    n 1: a person who specializes in designing architectural
         interiors and their furnishings [syn: interior designer,
         designer, interior decorator, house decorator, room
         decorator, decorator]
    2: someone who decorates [syn: decorator, ornamentalist]