English▸ verb
( naps, napping, napped)
[no object] (of a horse) refuse, especially habitually, to go on at the rider's instruction; jib: horses which nap should be dealt with by professionals.
– ORIGIN 1950s: back-formation from nappy, an adjective first used to describe heady beer (late Middle English), later used in the sense ‘intoxicated by drink’ (early 18th century), and since the 1920s used to describe a disobedient horse.