The Collaborative International Dictionary of English v.0.48:

Glottis \Glot"tis\, n. [NL., fr. Gr. ?, ?, from ?, ?, the
   tongue. See Gloss an explanatory remark.] (Anat.)
   The opening from the pharynx into the larynx or into the
   trachea. See Larynx.
   [1913 Webster]

WordNet (r) 3.0 (2006):

glottis
    n 1: the vocal apparatus of the larynx; the true vocal folds and
         the space between them where the voice tone is generated