The Collaborative International Dictionary of English v.0.48:

Nacre \Na"cre\ (n[=a]"k[~e]r), n. [F., cf. Sp. n['a]cara,
   n['a]car, It. nacchera, naccaro, LL. nacara, nacrum; of
   Oriental origin, cf. Ar. nak[imac]r hollowed.] (Zool.)
   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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Nacker \Nack"er\ (n[a^]k"[~e]r), n.
   See Nacre. --Johnson.
   [1913 Webster]