Cooked Dover sole (4)
I believe the answer is:
done
'cooked' is the definition.
(similar in meaning)
'dover sole' is the wordplay.
'dover' becomes 'd' (this could be a standard abbreviation of which I'm unaware).
'sole' becomes 'one' (synonyms).
'd'+'one'='DONE'
(Other definitions for done that I've seen before include "Completed" , "This sort of thing is socially acceptable" , "Swindled" , "that may be said to seal a deal" , "Achieved" .)