epiglottis

from WordNet (r) 3.0 (2006)

epiglottis
    n 1: a flap of cartilage that covers the windpipe while
         swallowing

from The Collaborative International Dictionary of English v.0.48

Epiglottis \Ep`i*glot"tis\, n. [NL., fr. Gr. ?; 'epi` upon + ?,
   ?, tongue. See {Glottis}.] (Anat.)
   A cartilaginous lidlike appendage which closes the glottis
   while food or drink is passing while food or drink is passing
   through the pharynx.
   [1913 Webster]