Nacre (6-2-5)
I believe the answer is:
mother-of-pearl
'nacre' is the definition.
(I know that nacre can be written as mother-of-pearl)
This is the entire clue.
(Other definitions for mother-of-pearl that I've seen before include "Decorative substance got from certain molluscs" , "Internal layer of shell" , "Nacre" , "Ornamental material" , "Iridescent material used in ornamentation" .)