Show disapproval when the booze is cut short (3)

I believe the answer is:

boo

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'show disapproval' is the definition.
(as in a crowd booing)

I don't understand how the rest of the clue works.

(Other definitions for boo that I've seen before include "Voice disapproval" , "I disapprove" , "Sound made to show disapproval or contempt" , "Disapproving sound" , "Startling utterance" .)

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

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