Trade fairs with English diamonds on show (7)
I believe the answer is:
exposed
'on show' is the definition.
(both can mean revealed to view)
'trade fairs with english diamonds' is the wordplay.
'trade fairs' becomes 'expos' (short for exposition, a large exhibition).
'with' means one lot of letters go next to another.
'english' becomes 'E' (abbreviation).
'diamonds' becomes 'd' (abbreviation in bridge say).
'expos'+'e'+'d'='EXPOSED'
(Other definitions for exposed that I've seen before include "Unmasked, revealed" , "Not hidden" , "Not covered" , "With no protection or shield" , "Shown up" .)