The Collaborative International Dictionary of English v.0.48:

Tortilla \Tor*til"la\, n. [Sp.]
   An unleavened cake, as of maize flour, baked on a heated iron
   or stone.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tortilla
    n 1: thin unleavened pancake made from cornmeal or wheat flour