Impact, n.
1. Contact or impression by touch; collision; forcible contact; force communicated. The quarrel, by that impact driven. Southey.
2. (Mech.)
The single instantaneous stroke of a body in motion against another either in motion or at rest.
1 other Webster entry under this spelling
Impact, v. t. [imp. & p. p. Impacted; p. pr. & vb. n. Impacting.]
To drive close; to press firmly together: to wedge into a place. Woodward.
Shades of meaning
Fernald has no entry of its own for impact; he lists it under collision.
Where he writes about it:
Concussion is often by transmitted force rather than by direct impact; two railway-trains come into collision; an explosion of dynamite shatters neighboring windows by concussion. — from collision
Impact is the blow given by the striking body; as, the impact of the cannon-shot upon the target. — from collision