mother-of-pearl (nacre) Shiny substance lining many mollusc shells. It consists of a form of calcium carbonate, deposited in layers interspersed with organic material. Diffraction of light causes the lustre and iridescence of mother-of-pearl. It is used in making buttons and jewellery, and for decorative inlay.

moth·er-of-pearl • n. a smooth shining iridescent substance forming the inner layer of the shell of some mollusks, esp. oysters and abalones, used in ornamentation.