retard

Etymology

From Middle English retarden, from Anglo-Norman or Latin, from Anglo-Norman retarder, from Latin retardāre (“to retard”), from re- + tardus (“slow”).

noun

1. Retardation; delay.
2. (music) A slowing down of the tempo; a ritardando.
3. (offensive, dated) A person with mental retardation.
   The retard in our class needs special help.
4. (informal, offensive) A person or being who is extremely stupid or slow to learn.
   “That's 'cause your dog is a retard,” the large woman retorted. The pit bull must have sensed the insult because it got up on all fours and started barking at the woman. Not one to back down from an interspecies fight, the prison lady stood up […] 2007, Doug Green, No Wife No Kids No Plan

verb

1. (transitive) To keep delaying; to continue to hinder; to prevent from progressing.
   retard the march of an army
   retard the motion of a ship
2. (transitive) To put off; to postpone.
   to retard the attacks of old age
   to retard a rupture between nations
3. (transitive, obsolete) To be slow or dilatory to perform (something).
4. (intransitive) To decelerate; to slow down.
   70, 60, 50, 40, 30, 20, retard, retard... 2019, Airbus A350 - Landing (Retard) (YouTube), cockpit voice (actor)
   This application of hydraulics led Sir George Dowty to develop the wagon retarder system, which comprised small hydraulic rams mounted inside the rail. These rams could simply retard a wagon, or both retard and 'boost' or speed up a wagon by hydraulic pressure. June 2 2021, Michael Rhodes, “Tinsley reborn...”, in RAIL, number 932, pages 35–36
5. (intransitive, obsolete) To stay back.