Break out in laughter up there (5)
I believe the answer is:
erupt
'break out' is the definition.
(synonyms)
'in laughter up there' is the wordplay.
'in' indicates a hidden word.
'ERUPT' is hidden within 'laughter up there'.
(Other definitions for erupt that I've seen before include "What canines do" , "Suddenly appear" , "Break out suddenly and violently" , "Blow up like volcano" , "Eject lava" .)