Cry of disapproval (3)

I think it could be either:

Which length description are you looking for?:

boo

'cry of disapproval' is the definition.
(I've seen this before)

This is all the clue.

(Other definitions for boo that I've seen before include "Surprising exclamation" , "Frightening word (for a goose?)" , "Cry of disapproval as at villain" , "I'm unimpressed" , "Startling utterance" .)

I've seen this clue in The Independent.

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