Late but not unwilling (7)
I believe the answer is:
testate
'late' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for testate that I've seen before include "Having written a valid will" , "Having made a will before death" , "Having left a legacy" , "State of having made a will" , "Having left valid will at death" .)