overhear 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.

Old English heran (Anglian), (ge)hieran, hyran (West Saxon) "to hear, perceive by the ear, listen (to), obey, follow; accede to, grant; judge," from Proto-Germanic *hausejanan (source also of Old Norse heyra, Old Frisian hera, hora, Dutch horen, German hören, Gothic hausjan "to hear"), from PIE root *kous- "to hear" (source also of Greek koein "to mark, perceive, hear;" see acoustic). The shift from *-s- to -r- is a regular feature in some Germanic languages. For the vowels, see head (n.).

Spelling distinction between hear and here developed 1200-1550. Meaning "be told, learn by report" is from early 14c. Old English also had the excellent adjective hiersum "ready to hear, obedient," literally "hear-some" with suffix from handsome, etc. Hear, hear! (1680s) originally was imperative, an exclamation to call attention to a speaker's words ("hear him!"); now a general cheer of approval. To not hear of "have nothing to do with" is from 1754.

late 14c., overloken, "to examine carefully, scrutinize, inspect," from over- + look (v.). Another Middle English sense was "to peer over the top of, survey from on high, view from a high place" (c. 1400).

These two literal senses have given rise to the two main modern meanings. The meaning "to look over or beyond and thus fail to see" (hence "to pass over indulgently") is via the notion of "to choose to not notice" and is attested from 1520s. The seemingly contradictory sense of "to watch over officially, keep an eye on, superintend" is from 1530s. Related: Overlooked; overlooking. In Shakespeare's day, overlooking also was a common term for "inflicting the evil eye on" (someone or something). Middle English had oure-loker (over-looker), meaning "a timekeeper in a monastery" (early 15c.).