Collision or conflict (5)
I believe the answer is:
clash
I believe this is a double definition.
'collision' is the first definition.
(thesaurus)
'conflict' is the second definition.
(I know that clash is a kind of conflict)
(Other definitions for clash that I've seen before include "Punk group; disagree" , "Disagree violently" , "Come together discordantly" , "Conflict, discord" , "Conflict; be incompatible" .)