Source : Webster's Revised Unabridged Dictionary (1913)

Nacre \Na"cre\, n. [F., cf. Sp. n['a]cara, n['a]car, It.
   nacchera, naccaro, LL. nacara, nacrum; of Oriental origin,
   cf. Ar. nak[=i]r hollowed.] (Zo["o]l.)
   A pearly substance which lines the interior of many shells,
   and is most perfect in the mother-of-pearl. [Written also
   {nacker} and {naker}.] See {Pearl}, and {Mother-of-pearl}.

Source : WordNet®

nacre
     n : the iridescent internal layer of a mollusk shell [syn: {mother-of-pearl}]