Hood left on farm animal (4)
I believe the answer is:
cowl
'hood' is the definition.
('cowl' can be a synonym of 'hood')
'left on farm animal' is the wordplay.
'left' becomes 'l' (common abbreviation).
'on' is a charade indicator (letters next to each other).
'farm animal' becomes 'cow' (I've seen this before).
'l' after 'cow' is 'COWL'.
(Other definitions for cowl that I've seen before include "Hood for monk or chimney" , "Dried fruit" , "Loose hood" , "Hood-shaped covering" , "form of protection?" .)