As a Noun: 1. Reduction in speed or rate. English = deceleration. 2. In mathematics and physics, the rate at which the speed of an object is decreasing. English = deceleration. As a Verb or Adjective: 1. To take your foot off the accelerator in order to make a vehicle go slower. English = slow down, decelerate. Idiomatic English = ease up, take one's foot off the brake. 2. To reduce or cause to reduce in speed. English = decelerate.