What does decelerate mean?
To decelerate means to reduce speed — either of oneself or of something else — making it the precise opposite of accelerate. The verb is used both transitively and intransitively: a driver may decelerate before a bend, while brakes decelerate the vehicle itself. Although rooted in physics and mechanics, where it describes any decrease in velocity, the word has extended naturally into figurative territory; economists speak of decelerating inflation or growth, for example. Decelerate carries a neutral, slightly technical tone, and in casual conversation speakers usually prefer the simpler phrase 'slow down'. Its derivatives include the noun deceleration, familiar from physics classrooms and space travel alike, where re-entry capsules rely on atmospheric drag for deceleration. Concise and unambiguous, the word is especially useful when a single verb is needed to describe a measured, deliberate reduction in pace rather than an abrupt halt.
verbTo reduce speed, or to cause something to move more slowly; the opposite of accelerate.
- (intransitive) To slow down or reduce speed.
- (transitive) To cause something, such as a vehicle or process, to decrease in speed or rate.
"The train began to decelerate as it approached the station platform."
"The aircraft decelerated sharply after touchdown on the runway."
"Economists noted that growth in consumer spending had decelerated over the final quarter."
Decelerate was born as a back-formation: people took 'deceleration' apart and built a verb from it — the opposite of how most words grow.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of decelerate
Decelerate derives from the Latin 'de-', indicating reduction or reversal, combined with 'celerare', from 'celer', meaning swift. It formed alongside its sibling 'accelerate', which shares the same Latin root via 'ad-' plus 'celerare' — the two words being exact opposites by prefix alone. Interestingly, 'decelerate' arose as a back-formation from the earlier noun 'deceleration', which entered English first, likely in the late 19th century. Cognates sharing the root include 'velocity' and 'celerity', both denoting swiftness.
Related word forms
How decelerate is actually used
Decelerate is common in technical and scientific contexts (physics, engineering, motoring) and also appears figuratively for slowing trends, such as economic growth. It is somewhat more formal than 'slow down' in everyday speech.
Easily confused with decelerate
Accelerate means to increase speed, while decelerate means to decrease speed — they are direct opposites.