Genuine piece of pure alabaster (4)
I believe the answer is:
real
'genuine' is the definition.
(associated in meaning)
'piece of pure alabaster' is the wordplay.
'piece of' indicates a hidden word.
'REAL' can be found hidden inside 'pure alabaster'.
(Other definitions for real that I've seen before include "Unaffected" , "True" , "'Genuine, actual (4)'" , "Actual, existing" , "The old coin actually exists" .)