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.
'left to him' is the wordplay.
'left' becomes 'leg' (left leg).
'to him' becomes 'atee' (I can't explain this - if you can you should believe this answer much more).
'leg'+'atee'='LEGATEE'
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" .)