Left fat pig inside (8)
I believe the answer is:
larboard
'left' is the definition.
(synonyms)
'fat pig inside' is the wordplay.
'fat' becomes 'lard' (lard is a kind of fat).
'pig' becomes 'boar' (I've seen this before).
'inside' indicates putting letters inside.
'lard' placed around 'boar' is 'LARBOARD'.
(Other definitions for larboard that I've seen before include "Side of ship for Labrador" , "Old term for port (naut.)" , "Left side of ship" , "left at sea" , "Port side" .)