Report collision (4)
I believe the answer is:
bang
This clue might be a double definition.
'report' is the first definition.
(report can mean a loud noise)
'collision' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for bang that I've seen before include "drug injection" , "Gun sound" , "precisely" , "Explosion; hair fringe" , "Explosive noise" .)