The Collaborative International Dictionary of English v.0.48:

Epicleidium \Ep`i*clei"di*um\, n. [NL., fr. Gr. 'epi` upon + ? a
   little key.] (Anat.)
   A projection, formed by a separate ossification, at the
   scapular end of the clavicle of many birds.
   [1913 Webster]