Source : Webster's Revised Unabridged Dictionary (1913)

Tref \Tref\, a. [Yiddish, fr. Heb. t[e^]r[=e]ph[=a]h an animal
   torn by wild beasts.]
   Ceremonially unclean, according to the Jewish law; -- opposed
   to {kosher}.

Source : WordNet®

tref
     adj : not conforming to dietary laws [syn: {nonkosher}, {terefah}]