Quiz: Remember the definition of mal de mer?
Old English slæpan "to be or fall asleep; be dormant or inactive" (class VII strong verb; past tense slep, past participle slæpen), from Proto-Germanic *slepan (cf. Old Saxon slapan, Old Frisian slepa, Middle Dutch slapen, Dutch slapen, Old High German slafen, German schlafen, Gothic slepan "to sleep"), from PIE root *sleb- "to be weak, sleep" (cf. Old Church Slavonic slabu "lax, weak," Lithuanian silpnas "weak"), which perhaps is connected to the root of slack (adj.). Sleep with "do the sex act with" is in Old English:
Gif hwa fæmnan beswice unbeweddode, and hire mid slæpe ... [Laws of King Alfred, c.900]Related: Slept; sleeping. Sleep around first attested 1928.
Old English slæp "sleep, sleepiness, inactivity," from Proto-Germanic *slepaz, from the root of sleep (v.); cf. cognate Old Saxon slap, Old Frisian slep, Middle Dutch slæp, Dutch slaap, Old High German slaf, German Schlaf, Gothic sleps.
Personified in English from late 14c., on model of Latin Somnus), Greek Hypnos. Figurative use for "repose of death" was in Old English; to put (an animal) to sleep "kill painlessly" is recorded from 1923 (a similar imagery is in cemetery). Sleep deprivation attested from 1906. Sleep-walker "somnambulist" is attested from 1747; sleep-walking is from 1840. To be able to do something in (one's) sleep "easily" is recorded from 1953.
A natural periodic state of rest for the mind and body, in which the eyes usually close and consciousness is completely or partially lost, so that there is a decrease in bodily movement and responsiveness to external stimuli. During sleep the brain in humans and other mammals undergoes a characteristic cycle of brain-wave activity that includes intervals of dreaming. v. slept (slěpt), sleep·ing, sleeps
To be in the state of sleep.
A natural, reversible state of rest in most vertebrate animals, occurring at regular intervals and necessary for the maintenance of health. During sleep, the eyes usually close, the muscles relax, and responsiveness to external stimuli decreases. Growth and repair of the tissues of the body are thought to occur, and energy is conserved and stored. In humans and certain other animals, sleep occurs in five stages, the first four consisting of non-REM sleep and the last stage consisting of REM sleep. These stages constitute a sleep cycle that repeats itself about five times during a normal episode of sleep. Each cycle is longer that the one preceding it because the length of the REM stage increases with every cycle until waking occurs. Stage I is characterized by drowsiness, Stage II by light sleep, and Stages III and IV by deep sleep. Stages II and III repeat themselves before REM sleep (Stage V), which occurs about 90 minutes after the onset of sleep. During REM sleep, dreams occur, and memory is thought to be organized. In the stages of non-REM sleep, there are no dreams, and brain activity decreases while the body recovers from wakeful activity. The amount and periodicity of sleep in humans vary with age, with infants sleeping frequently for shorter periods, and mature adults sleeping for longer uninterrupted periods. See also non-REM sleep, REM sleep.