Sabbath with high tea? (6)

I believe the answer is:

supper

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'tea?' is the definition.
(thesaurus)

'sabbath with high' is the wordplay.
'sabbath with' becomes 's' (I can't explain this - if you can you should give a lot more credence to this answer).
'high' becomes 'upper' ('upper' can be similar in meaning to 'high').
's'+'upper'='SUPPER'

Can you help me to learn more?

(Other definitions for supper that I've seen before include "Light, late, meal" , "Evening 2 Down" , "Light evening meal" , "has one had a few drinks?" , "Last meal of the day" .)

I've seen this clue in The Telegraph.

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