Cry of disapproval (3)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cry of disapproval</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(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" .)
(Other definitions for catcall that I've seen before include "Boo" , "Noisy expression of disapproval" , "Derisive call" , "1express disapproval" , "Shout of derision" .)