Simple stone set in gold before (7)
I believe the answer is:
austere
'simple' is the definition.
(I've seen this before)
'stone set in gold before' is the wordplay.
'stone' becomes 'st' (abbreviation).
'set in' is an insertion indicator.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'before' becomes 'ere' (poetic term).
'au'+'ere'='auere'
'st' going into 'auere' is 'AUSTERE'.
(Other definitions for austere that I've seen before include "Stern or very plain" , "Lacking adornments" , "Grim - USA tree (anag)" , "Severe; lacking luxuries" , "Severely simple and plain in appearance" .)