English speakers use sleep for the nightly drop in consciousness, for a stretch of rest, and, more loosely, for anything that has gone quiet: a computer, a numb limb, a question left unanswered. The verb can also mean to put someone up for the night, and it has long stood in for death and for sex. None of those extensions required a loanword. The origin of the word sleep is a native Germanic inheritance that was already in English before the Norman Conquest.
Inherited, not borrowed
The verb comes down through Middle English slepen from Old English slǣpan, with dialect variants slēpan in Anglian and slāpan in some West Saxon writing. The matching noun, Middle English slep, is Old English slǣp. Both are recorded in the Old English period, that is before 1150. They were not taken from French dormir or Latin somnus. They belong to the older stock of the language, the same layer as eat, drink, and wake.
Old English treated slǣpan as a strong verb of class VII. The past was slep, the past participle slæpen. That class had once formed its past by reduplication in Proto-Germanic; Gothic still shows a reduplicated past for this verb. By the time of written Old English the reduplication had faded, leaving a long vowel in the past. Later English mixed the old strong pattern with weak endings. Chaucer and Langland still have both kinds of past. Modern slept is the survivor: irregular, shortened, no longer a transparent class-VII form, but still not a regular -ed verb.
The Germanic stem
Behind the Old English pair sits Proto-West Germanic *slāpan and, further back, Proto-Germanic *slēpaną, reconstructed as to sleep. The noun is the related *slēpaz. The family is easy to see once you look across the North Sea. Dutch has slapen and slaap, German schlafen and Schlaf, Old Saxon slāpan, Old Frisian slēpa, West Frisian sliepe, Yiddish shlofn. Gothic, the earliest well-attested Germanic language, has slēpan as the verb and sleps as the noun. Crimean Gothic, recorded much later, still shows schlipen. These are sister forms, not borrowings into English.
The morphology is simple. There is no prefix to peel off and no Latin suffix hiding in the stem. Verb and noun grew from one Germanic root. English later added compounds and phrasal uses around that core, but the core itself is a short inherited verb.
An older root that will not sit still
Beyond Germanic the trail thins. Some dictionaries reconstruct a Proto-Indo-European *sleb- or *slēb- with a sense of being weak or sleeping. That reconstruction is sometimes linked, tentatively, to a slack root *sleg- or *(s)leh₁g-, the line that gives English slack from Old English slæc. Latin langueō, to be faint or listless, is occasionally brought into the same discussion. Baltic and Slavic words for weak, such as Lithuanian slābnas and the Slavic family behind Russian slabyi, have been cited as possible relatives of the weak/languid side of the comparison.
None of this is settled. Wiktionary’s reconstruction of *slēpaną calls the etymology unclear and notes that the verb may instead sit near Germanic *slapaz, weak or lax, itself of uncertain origin. Another proposal treats the sleep verb as a back-formation from related slack verbs. Older handbooks were more confident about a pre-Germanic *slēb- from *sleh₁-. Current specialist work is more cautious. The honest account is that English sleep is securely Germanic and only insecurely Indo-European.
What is not in doubt is that this is not the main ancient word for sleeping in Indo-European. That other root, *swep-, produced Latin somnus, Greek hypnos, Sanskrit svapiti, and a second Germanic verb *swefaną. Old English had that verb too, as swefan. Old Norse kept it as sofa, which is why modern Norwegian and Swedish still say sove and sova. English let swefan fall away and kept slǣpan. French dormir, from Latin dormīre, is a third, unrelated line. When English later borrowed somnolent, hypnotic, and dormitory, it was grafting those other families onto a native verb it had never lost.
How the senses stacked up
The core meaning, to rest with reduced consciousness, is already the Old English core. Around it the language piled figurative uses that have proved remarkably stable. To sleep could mean to lie dormant or inactive, to be careless when one should watch, and to rest in death. Christian writing in Old English already treated the dead as sleeping, the same metaphor that later English would use in cemetery, a word whose Greek source also played on the sleep of death. Numbness of a limb was another early extension: a foot or thigh that had gone dead was said to sleep. Sexual lying-with is equally old; it is not a modern euphemism layered onto a modest verb. Old English laws and biblical prose already use the verb that way.
Later centuries added more specific English idioms rather than a new core. To sleep on a decision, postponing it overnight, is recorded from the early sixteenth century. To sleep something off, waiting out drink or illness, appears in the eighteenth. Sleep in, remain in bed in the morning, is nineteenth-century. The transitive sense in which a room or tent sleeps four people is American English of the 1840s. Put to sleep as a euphemism for killing an animal painlessly is recorded from the 1880s. Sleep around is twentieth-century. Computing borrowed the verb twice: a process sleeps when it waits without working, and a machine sleeps when it powers down into a low-energy pause. The newest uses still lean on the oldest picture: activity stops, awareness drops, something waits.
The noun followed a similar path. Old English slǣp named the state, sleepiness, and inactivity. By about 1200 it could mean a stretch of sleep, a bout rather than the condition itself. Late Middle English personified Sleep on the model of Latin Somnus and Greek Hypnos. Dried matter in the corner of the eye, botanical folding of petals at night, and the computer’s low-power mode are later specializations of the same noun.
What English kept
The useful fact is the fork in Germanic. English, Dutch, German, and Gothic all rest on *slēpaną. The Scandinavian languages rest on *swefaną. English once had both and chose the first. That is why sleep looks like schlafen and slapen, not like sova, and why Latin somnus is a cousin of a verb English abandoned rather than of the verb it still uses every night.