Intended as the match of a lifetime (5)

I believe the answer is:

union

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'match of a lifetime' is the definition.
'union' can be an answer for 'match' (I've seen this before). I'm unsure of the 'of a lifetime' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for union that I've seen before include "Result of joining" , "Workers' organisation or marriage" , "Marriage; pipe joint" , "Wedding, say" , "Association with a common purpose" .)

I've seen this clue in The Globe and Mail.

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