Join jolly adult for bit of entertainment (5)

I believe the answer is:

marry

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'join' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for marry that I've seen before include "Join - get wed" , "expression of surprise once" , "Tie the knot; why! (Shak.)" , "Get hitched" , "Well I never!" .)

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