Lord, say, invading position (5)
I believe the answer is:
liege
'lord' is the definition.
(I have seen 'Feudal lord' mean 'liege' so perhaps 'lord' could also mean 'liege')
'say invading position' is the wordplay.
'say' becomes 'eg'.
'invading' is an insertion indicator.
'position' becomes 'lie' (lie is a kind of position).
'eg' going within 'lie' is 'LIEGE'.
(Other definitions for liege that I've seen before include "Faithful," , "On about one East Belgium city" , "Loyal subject" , "Owing feudal allegiance" , "Belgian city on Meuse" .)