The Collaborative International Dictionary of English v.0.48:

fire-retardant \fire-retardant\ adj.
   able to reduce combustibility or slow the spread of fire; --
   of substances that are added to combustible materials to make
   them less combustible.
   PJC]

WordNet (r) 3.0 (2006):

fire-retardant
    adj 1: difficult to burn [syn: fire-retardant, fire-
           resistant, fire-resisting, fire-resistive]