Etymology
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knowledge (n.)

early 12c., cnawlece "acknowledgment of a superior, honor, worship;" for first element see know (v.). The second element is obscure, perhaps from Scandinavian and cognate with the -lock "action, process," found in wedlock.

From late 14c. as "capacity for knowing, understanding; familiarity;" also "fact or condition of knowing, awareness of a fact;" also "news, notice, information; learning; organized body of facts or teachings." Sense of "sexual intercourse" is from c. 1400. Middle English also had a verb form, knoulechen "acknowledge" (c. 1200), later "find out about; recognize," and "to have sexual intercourse with" (c. 1300); compare acknowledge.

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gap (n.)

early 14c., "an opening in a wall or hedge; a break, a breach," mid-13c. in place names, from Old Norse gap "chasm, empty space," related to gapa "to gape, open the mouth wide," common Proto-Germanic (cognates: Middle Dutch, Dutch gapen, German gaffen "to gape, stare," Swedish gapa, Danish gabe), from PIE root *ghieh- "to yawn, gape, be wide open."

From late 14c. as "a break or opening between mountains;" broader sense "unfilled space or interval, any hiatus or interruption" is from c. 1600. In U.S., common in place names in reference to a deep break or pass in a long mountain chain (especially one that water flows through), a feature in the middle Appalachians.

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gap (v.)

1847, "to make gaps" (transitive); 1948 "to have gaps" (intransitive), from gap (n.). Related: Gapped; gapping.

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gap-toothed (adj.)

"having teeth set wide apart," 1570s, from gap (n.) + toothed "having teeth" (of a certain kind); see tooth (n.). Chaucer's gat-toothed, sometimes altered to this, is from Middle English gat (n.) "opening, passage," from Old Norse gat, cognate with gate (n.).

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stopgap (n.)

also stop-gap, 1680s, from stop (v.) + gap (n.); the notion probably being of something that plugs a leak, but it may be in part from gap (n.) in a specific military sense "opening or breach in defenses by which attack may be made" (1540s). Also as an adjective from 1680s.

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gappy (adj.)

"full of gaps," 1846, from gap (n.) + -y (2).

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void (n.)

1610s, "unfilled space, gap," from void (adj.). Meaning "absolute empty space, vacuum" is from 1727.

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epistemic (adj.)

"pertaining to knowledge," 1886, from Greek episteme "knowledge," especially scientific knowledge (see epistemology) + -ic.

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hiatus (n.)

1560s, "break or opening" in a material object, especially in anatomy, from Latin hiatus "opening, aperture, rupture, gap," from past participle stem of hiare "to gape, stand open," from PIE root *ghieh- "to yawn, gape, be wide open." Sense of "gap or interruption in events, etc.;" "space from which something requisite to completeness is absent" [Century Dictionary] is recorded from 1610s.

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omniscient (adj.)

"possessing knowledge of all things, having universal knowledge," c. 1600, from Modern Latin omniscientem (nominative omnisciens) "all-knowing," a back-formation from Medieval Latin omniscientia "all-knowledge," from Latin omnis "all" (see omni-) + scientia "knowledge" (see science). Related: Omnisciently.

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