Do not wed fool or knight or Old Nick (5,2,6)

I believe the answer is:

tower of london

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'old nick' is the definition.
Both the definition and answer are singular nouns.
Maybe they are linked in a way I don't understand?

'do not wed fool or knight' is the wordplay.
'do' indicates an anagram (solvers must work out or 'do' the anagram puzzle).
'knight' becomes 'N' (chess abbreviation).
'not'+'wed'+'fool'+'or'='notwedfoolor'
'notwedfoolor' with letters rearranged gives 'toweroflondo'.
'toweroflondo'+'n'='TOWER OF LONDON'

'or' acts as a link.

Can you help me to learn more?

(Other definitions for tower of london that I've seen before include "Capital's castle" , "Building" , "Where the Crown Jewels are kept" , "Home to the UK's Crown jewels" , "C eleven capital fortress" .)

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

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