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.
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.
1847, "to make gaps" (transitive); 1948 "to have gaps" (intransitive), from gap (n.). Related: Gapped; gapping.
1610s, "unfilled space, gap," from void (adj.). Meaning "absolute empty space, vacuum" is from 1727.
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.
"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.