Mother-of-pearl (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
nacre
'mother-of-pearl' is the definition.
(I know that mother-of-pearl can be written as nacre)
This is all the clue.
(Other definitions for nacre that I've seen before include "inside of shell" , "Constituent of inlay furniture" , "valuable material" , "Pearl's mum" , "Mother of pearl" .)