Crossword Genius

Sound of disapproval (3)

Ross

There are a few possibilities for this:

'sound of disapproval' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for boo that I've seen before include "Surprising exclamation" , "A shocking exclamation!" , "Shout in disgust" , "Startling utterance" , "Disapproving jeer" .)

I've seen this clue in the USA Today, the Evening Standard, the Newsday, The Mirror, the Universal, the LA Times and The Wall Street Journal.
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