"a spending of a night in a place other than one's residence," 1935, from the verbal phrase; see sleep (v.) + over (adv.). Earlier the verbal phrase meant "sleep late, oversleep" (1827).
Entries linking to sleep-over
sleep v.
Middle English slepen, from Old English slæpan "to be or fall asleep; lie or remain dormant or inactive" (class VII strong verb; past tense slep, past participle slæpen), from Proto-Germanic *slēpanan (source also of Old Saxon slapan, Old Frisian slepa, Middle Dutch slapen, Dutch slapen, Old High German slafen, German schlafen, Gothic slepan "to sleep"), from PIE *sleb- "to be weak, sleep," which perhaps is connected to root *sleg- "be slack, be languid," the source 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. There is no cognate form of the verb in Scandinavian. The usual PIE root is *swep-. The meaning "to rest as in the grave" is from Old English. In reference to parts of the body, "be numb through stoppage of circulation," late Old English. The sense of "provide or afford sleeping accommodations for" is by 1848, American English.
To sleep in "remain in bed in the morning" is by 1827; to sleep out "spend the night in the open" is by 1852. To sleep (something) off "remove the effects of by sleeping" is from 1760 (sleep out in the same sense is from 1550s). To sleep on some matter "postpone decision until the following day" is from 1510s, perhaps suggesting guidance in a dream. To sleep around "have casual sex with multiple partners" is attested by 1928.
over prep., adv.
Old English ofer "beyond; above, in place or position higher than; upon; in; across, past; more than; on high," from Proto-Germanic *uberi (source also of Old Saxon obar, Old Frisian over, Old Norse yfir, Old High German ubar, German über, Gothic ufar "over, above"), from PIE root *uper "over."
As an adjective from Old English uffera. The senses of "past, done, finished; through the whole extent, from beginning to end" are attested from late 14c. The sense of "so as to cover the whole surface" is from c. 1400. Meaning "leaning forward and down" is from 1540s. The meaning "recovered from" is from 1929. In radio communication, it is used to indicate the speaker has finished speaking (1926).
Above expresses greater elevation, but not necessarily in or near a perpendicular direction; over expresses perpendicularity or something near it: thus, one cloud may be above another, without being over it. Over often implies motion or extension where above would not; hence the difference in sense of the flying of a bird over or above a house, the hanging of a branch over or above a wall. In such uses over seems to represent greater nearness. [Century Dictionary]
Phrase over and above (mid-15c.) is pleonastic, for emphasis. Adjective phrase over-the-counter is attested from 1875, originally of stocks and shares. To be (someone) all over "be exactly what one expects of (someone)" is by 1721.