Real Dictionary

impact
The impact that something has on a situation, process, or person is a sudden and powerful effect that it has on them.
variable noun: An impact is the action of one object hitting another, or the force with which one object hits another.
verb: If one object impacts on another, it hits it with great force.
verb: To impact on a situation, process, or person means to affect them.

impact in American English
to force tightly together; pack; wedge
intransitive verb: to have impact or make contact forcefully
noun: the striking of one thing against another; forceful contact; collision
transitive verb: to drive or press closely or firmly into something; pack in

impact in Automotive Engineering
noun: An impact is the action of a vehicle hitting another vehicle or object, or the force with which one hits the other.

impact in British English
noun: the act of one body, object, etc, striking another; collision
verb: to drive or press (an object) firmly into (another object, thing, etc) or (of two objects) to be driven or pressed firmly together

impact in Mechanical Engineering
noun: Impact is the sudden application of a force.