Ring on bishop, with gemstone, ornamental article (5)
I believe the answer is:
objet
'ornamental article' is the definition.
(as in an objet d'art)
'ring on bishop with gemstone' is the wordplay.
'ring' becomes 'o' (letter resembling a ring).
'on' says to put letters next to each other.
'bishop' becomes 'B' (chess abbreviation).
'with' is a charade indicator (letters next to each other).
'gemstone' becomes 'jet' (jet is a type of stone).
'o'+'b'+'jet'='OBJET'
(Other definitions for objet that I've seen before include "An - d'art is an artistic piece" , "item in French" .)