The Collaborative International Dictionary of English v.0.48:

nonfunctional \nonfunctional\ adj.
   1. Not having or performing a function. [Narrower terms:
      cosmetic, decorative, ornamental ] Also See:
      {unserviceable. functional
      [WordNet 1.5]

   2. Not performing or able to perform its regular function;
      as, the yard was littered with nonfunctional vehicles
      waiting to be repaired. [Narrower terms: down(predicate)
      ]. Antonym: {functioning.

   Syn: malfunctioning, unserviceable, out of order.
        [WordNet 1.5] nonglutenous

WordNet (r) 3.0 (2006):

nonfunctional
    adj 1: not having or performing a function [ant: functional]
    2: not performing or able to perform its regular function; "a
       malfunctioning valve" [syn: malfunctioning,
       nonfunctional] [ant: functioning]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "nonfunctional":
   functionless, impractical, in disrepair, inapplicable, inoperable,
   inoperative, nonutilitarian, otiose, out of order, out of whack,
   unconducive, unemployable, unfit, unhelpful, unserviceable,
   unsuitable, unusable, unworkable