Picture left — one nibbled by rodent? (8)
I believe the answer is:
portrait
'picture' is the definition.
(portrait is a type of picture)
'left one nibbled by rodent?' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'one' becomes 'i' (Roman numeral).
'nibbled by' is an insertion indicator.
'rodent?' becomes 'rat' (rat is a kind of rodent).
'i' inserted into 'rat' is 'rait'.
'port'+'rait'='PORTRAIT'
(Other definitions for portrait that I've seen before include "Type of painting" , "Person's picture" , "characteristic depiction" , "Depiction of person" , "Oil perhaps" .)