Landed gentleman holding right large rodent (8)
I believe the answer is:
squirrel
'rodent' is the definition.
(I know that squirrel is a type of rodent)
'landed gentleman holding right large' is the wordplay.
'landed gentleman' becomes 'squire'.
'holding' is an insertion indicator.
'right' becomes 'r' (common abbreviation).
'large' becomes 'L' (eg in clothes sizes).
'squire' placed around 'r' is 'squirre'.
'squirre'+'l'='SQUIRREL'
(Other definitions for squirrel that I've seen before include "Nut-gathering rodent" , "Gnawing animal" , "Tree-dwelling rodent" , "Brown or red rodent" , "hide away" .)