Etymology
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edge (v.)

late 13c., "to give an edge to" (implied in past participle egged), from edge (n.). Intransitive meaning "to move edgeways (with the edge toward the spectator), advance slowly" is from 1620s, originally nautical. Meaning "to defeat by a narrow margin" is from 1953. The meaning "urge on, incite" (16c.) often must be a mistake for egg (v.). Related: Edger.

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knife (n.)

"hand-held cutting instrument consisting of a short blade and handle," late Old English cnif, probably from Old Norse knifr "knife, dirk," from Proto-Germanic *knibaz (source also of Middle Low German knif, Middle Dutch cnijf, German kneif), a word of uncertain origin. To further confuse the etymology, there also are forms in -p-, such as Dutch knijp, German kneip. French canif "penknife" (mid-15c.) is probably of Germanic origin, perhaps from Frankish. For pronunciation, see kn-.

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edge (n.)

Old English ecg "corner, edge, point," also "sword" (also found in ecgplega, literally "edge play," ecghete, literally "edge hate," both used poetically for "battle"), from Proto-Germanic *agjo (source also of Old Frisian egg "edge;" Old Saxon eggia "point, edge;" Middle Dutch egghe, Dutch eg; Old Norse egg, see egg (v.); Old High German ecka, German Eck "corner"), from PIE root *ak- "be sharp, rise (out) to a point, pierce."

Spelling development of Old English -cg to Middle English -gg to Modern English -dge represents a widespread shift in pronunciation. To get the edge on (someone) is U.S. colloquial, first recorded 1911. Edge city is from Joel Garreau's 1992 book of that name. Razor's edge as a perilous narrow path translates Greek epi xyrou akmes. To be on edge "excited or irritable" is from 1872; to have (one's) teeth on edge is from late 14c., though "It is not quite clear what is the precise notion originally expressed in this phrase" [OED].

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knife (v.)

1865, "stab or kill with a knife," from knife (n.). Intransitive meaning "move as a knife does" is from 1920. Related: Knifed; knifing.

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jack-knife (n.)

also jackknife, "pocket knife larger than a pen-knife," 1711, probably American English, apparently from some sense of jack (n.). Perhaps it originally was associated with sailors. Jackleg, jacklegged was a U.S. colloquial term of contempt from 1839. Scottish dialect had jockteleg (1670s) "large clasp-knife," of unknown origin, also jackylegs, jack-o-legs. As a kind of swimming dive from 1922; as a type of tractor-trailer accident, 1966; both from the notion of folding, as the knife does.

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clasp-knife (n.)

"knife with one or more blades which fold into the handle," 1743, from clasp (n.) + knife (n.). The thing itself was known to the Etruscans and Romans; it became popular again 17c. 

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case-knife (n.)

"knife carried in a sheath," 1704, from case (n.2) + knife (n.).

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jack-knife (v.)

1776, "to stab," from jack-knife (n.). Intransitive meaning "to fold or bend" the body is said to date from the time of the American Civil War. The truck accident verbal sense is from 1949. Related: Jackknifed; jackknifing.

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butcher-knife (n.)

"large, sharp, heavy knife used for cutting and trimming meat," 1822, from butcher (n.) + knife (n.). Butcher's knife is attested from 1714.

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straight-edge (n.)

1812, "bar for drawing or measuring straight lines," from straight (adj.1) + edge (n.). As the name of a punk subculture, attested by 1987, probably suggested by straight (adj.2).

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