The Collaborative International Dictionary of English v.0.48:

Stapes \Sta"pes\ (st[=a]"p[=e]z), n. [LL., a stirrup.] (Anat.)
   The innermost of the ossicles of the ear; the stirrup, or
   stirrup bone; -- so called from its form. See Illust. of
   Ear.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stapes
    n 1: the stirrup-shaped ossicle that transmits sound from the
         incus to the cochlea [syn: stapes, stirrup]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "stapes":
   Eustachian tube, anvil, auditory apparatus, auditory canal,
   auditory meatus, auditory nerve, auditory ossicles, auditory tube,
   auricle, basilar membrane, bony labyrinth, cauliflower ear,
   cochlea, conch, concha, drumhead, ear, ear lobe, eardrum,
   endolymph, external ear, hammer, incus, inner ear, lobe, lobule,
   lug, malleus, mastoid process, middle ear, organ of Corti,
   outer ear, oval window, perilymph, pinna, round window,
   secondary eardrum, semicircular canals, shell, stirrup,
   tympanic cavity, tympanic membrane, tympanum, vestibule