Lord to object to plan (10)
I believe the answer is:
mastermind
'plan' is the definition.
(masterminding is a kind of planning)
'lord to object' is the wordplay.
'lord' becomes 'master' ('master' can be a synonym of 'lord').
'to object' becomes 'mind' (minding is a kind of objecting**).
'master'+'mind'='MASTERMIND'
'to' is the link.
(Other definitions for mastermind that I've seen before include "Knowledge-testing TV quiz" , "Planning supremo" , "Brainy TV quiz" , "Person conceiving a project - TV programme" , "Be behind" .)