moth·er-of-pearl /ˌmʌðərə(v)ˈpɚ/
  珍珠母
  Moth·er-of-pearl n. Zool. The hard, iridescent, pearly internal layer of several kinds of shells, esp. of pearl oysters, river mussels, and the abalone shells; nacre. See Pearl.
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  mother-of-pearl
       n : the iridescent internal layer of a mollusk shell [syn: nacre]