1. The striking of one body against another; collision. See Synonyms at collision.
2. The force or impetus transmitted by a collision.
3. The effect or impression of one thing on another: still gauging the impact of automation on the lives of factory workers.
4. The power of making a strong, immediate impression: a speech that lacked impact.

1. To pack firmly together.
2. To strike forcefully: meteorites impacting the lunar surface.
3. Usage Problem To have an effect or impact on: "No region ... has been more impacted by emerging demographic and economic trends" (Joel Kotkin).

Usage Note: The use of impact as a verb meaning "to have an effect" often has a big impact on readers. In our 2001 survey, 85 percent of the Usage Panel disapproved of the construction to impact on, as in the sentence These policies are impacting on our ability to achieve success; fully 80 percent disapproved of the use of impact as a transitive verb in the sentence The court ruling will impact the education of minority students. · It is unclear why this usage provokes such a strong response, but it cannot be because of novelty. Impact has been used as a verb since 1601, when it meant "to fix or pack in," and its modern, figurative use dates from 1935. It may be that its frequent appearance in the jargon-riddled remarks of politicians, military officials, and financial analysts continues to make people suspicious. Nevertheless, the verbal use of impact has become so common in the working language of corporations and institutions that many speakers have begun to regard it as standard. It seems likely, then, that the verb will eventually become as unobjectionable as contact is now, since it will no longer betray any particular pretentiousness on the part of those who use it. See Usage Note at contact.