decelerate

To decelerate means to decrease in speed or rate. It's most commonly used when describing physical motion—such as a car decelerating as it approaches a stop sign or a runner easing up at the end of a race. For example: "The train began to decelerate as it entered the station."

However, decelerate isn't limited to physical objects! It frequently describes a slowing of progress, growth, or activity. You will often see it in news headlines: "Economic growth is expected to decelerate next year," meaning the rate of growth will diminish. Or, "The company decided to decelerate its expansion plans due to market uncertainty."

In everyday conversation, decelerate often sounds more formal than the simple phrase "slow down." You're more likely to use it when the slowing is deliberate, measured, or described in a technical way—like braking, a spacecraft decelerating, or a process being carefully controlled. You might also see it used for abstract things: a market, a schedule, or the rate of a chemical reaction can decelerate.

In technical writing, the idea is closely tied to acceleration (a change in speed): to decelerate is to accelerate in a way that reduces speed. In everyday English, you can usually treat it as a more formal way to say "slow down."

So, whether it's a vehicle, an economy, or a project timeline, to decelerate is to reduce speed or rate—often with intention, and sometimes indicating a shift from rapid growth to a more sustainable pace.