The Collaborative International Dictionary of English v.0.48:

Gristle \Gris"tle\, n. [OE. gristel, gristil, AS. gristl; akin
   to OFries. gristel, grestel. Perh. a dim. of grist but cf.
   OHG. krustila, krostela. Cf. Grist.] (Anat.)
   Cartilage. See Cartilage. --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gristle
    n 1: tough elastic tissue; mostly converted to bone in adults
         [syn: cartilage, gristle]