A hot concoction to swear by? (4)

I believe the answer is:

oath

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'swear by?' is the definition.
'oath' can be an answer for 'swear' (thesaurus). I am not sure about the 'by?' bit.

'a hot concoction' is the wordplay.
'concoction' is an anagram indicator.
'a'+'hot'='ahot'
'ahot' with letters rearranged gives 'OATH'.

'to' acts as a link.

Can you help me to learn more?

(Other definitions for oath that I've seen before include "A curse or solemn declaration" , "Solemn promise to tell the truth or be loyal" , "What frustrated people say" , "Vow, sworn word" , "Vow or expletive" .)

I've seen this clue in the Evening Standard.

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