Suppress onset of laughter in unfamiliar setting (8)
I believe the answer is:
Here is my best explanation:
'suppress' is the definition.
'onset of laughter in unfamiliar setting' is the subsidiary indication.
'onset of' says to take the initial letters.
'in' is an insertion indicator.
'unfamiliar setting' becomes 'strange'.
The first letter of 'laughter' is 'l'.
'l' inserted within 'strange' is 'strangle'.
(Other definitions for strangle that I've seen before include "kill", "Asphyxiate, throttle", "Kill by throttling", "gag", "Tanglers who suffocate", "Throttle", "Tanglers - asphyxiate them", "Finish off", "Smother" and "suppress".)