The Collaborative International Dictionary of English v.0.48:

Designer \De*sign"er\, n.
   1. One who designs, marks out, or plans; a contriver.
      [1913 Webster]

   2. (Fine Arts) One who produces or creates original works of
      art or decoration.
      [1913 Webster]

   3. A plotter; a schemer; -- used in a bad sense.
      [1913 Webster]

WordNet (r) 3.0 (2006):

designer
    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 creates plans to be used in making something
       (such as buildings) [syn: architect, designer]
    3: someone who specializes in graphic design [syn: graphic
       designer, designer]
    4: a person who devises plots or intrigues; "he is believed to
       be the principal designer of the terrorist bombing attack"
       [syn: designer, intriguer]
    5: someone who designs clothing [syn: couturier, fashion
       designer, clothes designer, designer]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "designer":
   a, ancestors, apprentice, architect, artificer, artist, author,
   begetter, beginner, builder, conceiver, conniver, conspirator,
   constructor, contriver, costume designer, couturier, craftsman,
   creator, developer, deviser, discoverer, draughtsman,
   dress designer, effector, engenderer, engineer, enterpriser,
   entrepreneur, executor, executrix, father, founder, framer,
   furniture designer, generator, grower, inaugurator, industrialist,
   initiator, instigator, institutor, intriguer, introducer, inventor,
   journeyman, maker, manufacturer, master, master craftsman, mother,
   organizer, originator, past master, planner, plotter, precursor,
   prime mover, producer, projector, promoter, raiser, realizer,
   rug designer, schemer, shaper, sire, smith, strategian, strategist,
   styler, stylist, tactician, wright