Drink to celebrate retirement? (8)

I believe the answer is:

nightcap

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'drink' is the definition.
(nightcap is a kind of drink)

I don't understand the rest of the clue.

(Other definitions for nightcap that I've seen before include "Last drink before bed" , "attire" , "drink having sleepy effect?" , "Patching up with drink at bedtime" , "Pre-bed drink" .)

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

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