See collision in Webster's New World College Dictionary
noun
the act of colliding, or coming together with sudden, violent force
a clash or conflict of opinions, interest, etc.
See collision in American Heritage Dictionary 4
(kə-lĭzhˈən)
noun
The act or process of colliding; a crash or conflict.
Physics A brief dynamic event consisting of the close approach of two or more particles, such as atoms, resulting in an abrupt change of momentum or exchange of energy.