What does retarder mean?
A retarder is a device designed to reduce speed, most often a heavy-duty mechanism used in vehicles to assist braking. An exhaust retarder, for example, uses resistance created by the engine to help slow a truck on a descent. The word also has an older sense meaning a person who delays something or holds back progress, but that usage is now rarely acceptable and can be seriously offensive when directed at a person with an intellectual disability. In contemporary technical and transport contexts, however, “retarder” normally refers clearly to the speed-control device rather than to a person. It is related in origin to “retard,” “retardant,” and “retardation,” all of which involve slowing, delaying, or impeding something.
A device that reduces speed, especially a braking or engine-braking device used in heavy vehicles.
"The vehicle's electronic retarder helped the driver maintain a safe speed."
Common in road transport, trucking, and railway contexts.
A person who delays something or holds back progress.
"The wording used in the old document is outdated and should not be repeated as a description of a person."
Obsolete in general use and potentially offensive, especially when used to refer to a person with an intellectual disability.
The plural is used when referring to multiple speed-control devices or multiple people using the now-outdated person sense.
"Several vehicles were fitted with electronic retarders."
Trucking's invisible helper is an exhaust retarder: it uses the engine's braking resistance to help slow a heavy vehicle without relying solely on the service brakes.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does retarder come from?
The word comes through French from the Latin verb retardare, meaning “to delay” or “to hold back,” ultimately from tardus, meaning “slow.” English borrowed the form in the sense of delaying or slowing an action or process. The later mechanical sense developed from the broader idea of making movement or speed less, and in transport usage it refers to a device that assists braking.
Related word forms
How retarder is actually used
In modern English, the mechanical sense is usual. The sense meaning a person who delays something is rarely appropriate and should be avoided, especially when it is intended to stigmatize a person with an intellectual disability; in that context, language describing a specific characteristic or need is preferable.
Easily confused with retarder
A retarder reduces the speed of a vehicle or other moving mechanism, whereas a retardant delays a chemical process, such as combustion or the spread of flame.