Everything may be left to him (7)
I believe the answer is:
legatee
'everything may be left to him' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is all the clue.
Can you help me to learn more?
(Other definitions for legatee that I've seen before include "One coming into property" , "Recipient of a bequest" , "man newly-enriched?" , "One receiving legacy" , "person entitled to benefit" .)