Lark's head in front of rook (5)
I believe the answer is:
caper
'lark's' is the definition.
(I've seen this before)
'head in front of rook' is the wordplay.
'head' becomes 'cape' (both can mean a piece of land jutting over the sea).
'in front of' indicates taking the first letters.
The initial letter of 'rook' is 'r'.
'cape'+'r'='CAPER'
(Other definitions for caper that I've seen before include "Ridiculous escapade" , "Frolic, prank" , "Flower bud used in cooking" , "One likely to get pickled" , "Frolic - bud used in cooking" .)