Join you the night after, say (5)

I believe the answer is:

unite

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'join' is the definition.
(I know that join can be written as unite)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for unite that I've seen before include "Pull together" , "Gather together as one" , "Amalgamate" , "Link" , "Bring together, become one" .)

I've seen this clue in the Evening Standard.

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