WordNet (r) 3.0 (2006):

footrest
    n 1: a low seat or a stool to rest the feet of a seated person
         [syn: footstool, footrest, ottoman, tuffet]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "footrest":
   doorstep, foothold, footing, footplate, footrail, footstep, hold,
   locus standi, perch, purchase, rest, riser, round, rundle, rung,
   scale, spoke, stair, stance, stand, standing, standing place,
   stave, step, step stool, stepping-stone, string, toehold, tread