One leaving will finally get peace, say (7)
I believe the answer is:
testate
'one leaving will' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'finally get peace say' is the wordplay.
'finally' suggests the final letters.
'say' becomes 'state' (synonyms).
The last letters of 'get peace' are 'te'.
'te'+'state'='TESTATE'
Can you help me to learn more?
(Other definitions for testate that I've seen before include "Having made a last will and testament" , "State of having made a will" , "With a legally valid will" , "Dying with a will" , "Having made a legal will" .)