A spare part is capital! (5)

I believe the answer is:

paris

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'capital' is the definition.
(capital of France)

'a spare part is' is the wordplay.
'a spare part' becomes 'par' (I can't explain this - if you can you should believe this answer much more).
'par'+'is'='PARIS'

Can you help me to learn more?

(Other definitions for paris that I've seen before include "He abducted Helen of Troy" , "Prince who abducted Helen, starting a long war (see 8)" , "Arc de Triomphe city" , "Prince of Troy - capital city" , "Eiffel Tower city" .)

I've seen this clue in the Evening Standard.

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