Court sweetheart in empty declaration, emotionless (6)
I believe the answer is:
wooden
'emotionless' is the definition.
(I've seen this before)
'court sweetheart in empty declaration' is the wordplay.
'court' becomes 'woo' (both can mean to romance someone).
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'in' indicates putting letters inside.
'empty' says to hollow out the word (remove centre letters).
'declaration' with its middle taken out is 'dn'.
'e' going within 'dn' is 'den'.
'woo'+'den'='WOODEN'
(Other definitions for wooden that I've seen before include "Stiff as a board (when acting?)" , "Awkward, like a tree?" , "Lacking ease or grace, like a tree?" , "Ligneous" , "Unnatural (acting)" .)