Bond girl disheartened by European Union mirrors (4)
I believe the answer is:
glue
'bond' is the definition.
(I've seen this in another clue)
'girl disheartened by european union mirrors' is the wordplay.
'disheartened' suggests removing the centre (the middle or heart is removed).
'by' is a charade indicator (letters next to each other).
'european union' becomes 'eu' ().
'mirrors' is a reversal indicator (I've seen 'mirrored' mean this).
'girl' with its middle taken out is 'gl'.
'eu' backwards is 'ue'.
'gl'+'ue'='GLUE'
(Other definitions for glue that I've seen before include "Fixative" , "Sticky substance" , "size" , "agent with sticking power" , "Adhesive stuff" .)