Crossword Genius

Having finally left everything one can leave (7)

Ross

I believe the answer is:

testate

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'leave' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

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 made a last will and testament" , "Having made a will before death" , "Person willing" , "Having made a legal will" , "Having left valid will at death" .)

I've seen this clue in The Times.
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