Crossword Genius

Mortuus est, vitam reliquit; lit. he has gone down (8)

Ross

I believe the answer is:

decessit

I'm a little stuck... Click here to teach me more about this clue!

'mortuus est vitam reliquit lit' is the definition.
I know nothing about this answer so I can't judge whether this works.

'he has gone down' is the wordplay.
I cannot really see how this works, but
'he' could be 'si' and 'si' is found within the answer.
'down' could be 'd' and 'd' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Times.
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