Crow and lark's head covered in butter (5)
I believe the answer is:
gloat
'crow' is the definition.
(synonyms)
'lark's head covered in butter' is the wordplay.
'head' says to take the initial letters.
'covered in' is an insertion indicator.
'butter' becomes 'goat' (a goat is a butt-er).
The initial letter of 'larks' is 'l'.
'l' put inside 'goat' is 'GLOAT'.
'and' acts as a link.
(Other definitions for gloat that I've seen before include "Crow over" , "Look triumphant" , "Take malicious satisfaction" , "Exult maliciously" , "Express triumphant self-satisfaction" .)