The Collaborative International Dictionary of English v.0.48:

Gristly \Gris"tly\, a. (Anat.)
   Consisting of, or containing, gristle; like gristle;
   cartilaginous.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gristly
    adj 1: difficult to chew [syn: cartilaginous, gristly,
           rubbery]