Invest with right to last (6)
I believe the answer is:
endure
'last' is the definition.
('endure' can be a synonym of 'last')
'invest with right' is the wordplay.
'invest' becomes 'endue' ('endue' can be a synonym of 'invest').
'with' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'endue' going around 'r' is 'ENDURE'.
'to' acts as a link.
(Other definitions for endure that I've seen before include "Stand" , "Last or undergo" , "'Last, bear (6)'" , "Put up with or withstand" , "Abide" .)