oversleep v.

word-forming element meaning variously "above; highest; across; higher in power or authority; too much; above normal; outer; beyond in time, too long," from Old English ofer (from PIE root *uper "over"). Over and its Germanic relations were widely used as prefixes, and sometimes could be used with negative force. This is rare in Modern English, but compare Gothic ufarmunnon "to forget," ufar-swaran "to swear falsely;" Old English ofercræft "fraud."

In some of its uses, moreover, over is a movable element, which can be prefixed at will to almost any verb or adjective of suitable sense, as freely as an adjective can be placed before a substantive or an adverb before an adjective. [OED]

Among the old words not now existing are Old English oferlufu (Middle English oferlufe), literally "over-love," hence "excessive or immoderate love." Over- in Middle English also could carry a sense of "too little, below normal," as in over-lyght "of too little weight" (c. 1400), overlitel "too small" (mid-14c.), oversmall (mid-13c.), overshort, etc.

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.