Good health argument supporting rest (6)

I believe the answer is:

prosit

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'good health' is the definition.
(German toast for drinking someone's health)

'argument supporting rest' is the wordplay.
'argument' becomes 'pro' (pro is a kind of argument).
'supporting rest' becomes 'sit' (I've seen this in other clues. I am not sure about the 'supporting' bit.).
'pro'+'sit'='PROSIT'

Can you help me to learn more?

(Other definitions for prosit that I've seen before include "Happy days, perhaps" , "Bottoms up (in Germany)" , "Drinking salutation" , "Good health!; tripos (anagram)" , "good health is the answer" .)

I've seen this clue in The Sunday Times and The Times.

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