Etymology
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razor (n.)

c. 1300, rasour, "sharp-edged instrument for shaving or cutting hair," from Old French rasor, raseor "a razor" (12c.), from raser "to scrape, shave," from Medieval Latin rasare, frequentative of Latin radere (past participle rasus) "to scrape, shave" (see raze (v.)). Compare Medieval Latin rasorium.

As a verb, by 1827 as "shave with a razor," 1937 as "assault with a razor." The razor clam (1835, American English) is so called because its shell resembles an old folding straight-razor. Razor edge, figurative of sharpness or a fine surface, is by 1680s. Razor-blade is attested by 1816.

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razorback (n.)

also razor-back, type of hog with a sharp ridge-like back, 1849, from razor (n.) + back (n.). Especially of feral hogs in the U.S. South. Also used of narrow ridges of land.

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Occam's razor (n.)

when two competing hypotheses explain the data equally well, choose the simpler. Or, as Sir William Hamilton puts it, "Neither more, nor more onerous, causes are to be assumed, than are necessary to account for the phenomena." Named for English philosopher William of Ockham or Occam (c. 1285-c. 1349), "The Invincible Doctor," who expressed it with Entia non sunt multiplicanda praeter neccssitatem.

So called after William of Occam (died about 1349): but, as a historical fact, Occam does not make much use of this principle, which belongs rather to the contemporary nominalist William Durand de St. Pourçain (died 1332). [Century Dictionary]
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*red- 

*rēd-, Proto-Indo-European root meaning "to scrape, scratch, gnaw."

It forms (possibly) all or part of: abrade; abrasion; corrode; corrosion; erase; erode; erosion; radula; rascal; rase; rash (n.) "eruption of small red spots on skin;" raster; rat; raze; razor; rodent; rostrum; tabula rasa.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit radati "scrapes, gnaws," radanah "tooth;" Latin rodere "to gnaw, eat away," radere "to scrape;" Welsh rhathu "scrape, polish."

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shaving (n.)
"act of removing hair with a razor," also "thin slice taken off," late 14c., verbal noun from shave (v.).
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shiv (n.)

"a razor," by 1915, possibly 1890s or earlier in underworld slang, a variant (based on pronunciation) of chive, thieves' cant word for "knife" (1670s), of unknown origin. Often said to be a Romany (Gypsy) word, from chivomengro "knife." 

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advertisement (n.)

early 15c., "written statement calling attention to (something), public notice" (of anything, but often of a sale); from Old French avertissement (15c., later respelled pedantically as advertissement, a change rejected in French but accepted in English), from stem of avertir "to turn, direct, make aware" (see advertise). Meaning "public notice (usually paid) in a newspaper or other publication," the main modern sense, emerged 1580s and was fully developed by 18c.; later extended to Web sites.

Advertisements are now so numerous that they are very negligently perused, and it is therefore become necessary to gain attention by magnificence of promises and by eloquence sometimes sublime and sometimes pathetick. Promise, large promise, is the soul of an advertisement. I remember a washball that had a quality truly wonderful—it gave an exquisite edge to the razor! ... The trade of advertising is now so near to perfection that it is not easy to propose any improvement. [Johnson, "The Idler," Jan. 20, 1758]
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safety (n.)

early 14c., savete, "freedom or immunity from harm or danger; an unharmed or uninjured state or condition," from Old French sauvete, salvete "safety, safeguard; salvation; security, surety," earlier salvetet (11c., Modern French sauveté), from Medieval Latin salvitatem (nominative salvitas) "safety," from Latin salvus "uninjured, in good health, safe" (from PIE root *sol- "whole, well-kept"). From late 14c. as "means or instrument of safety, a safeguard."

The meaning "trigger-lock on a gun" is attested by 1881, perhaps short for safety-lock (1877), etc. As a North American football position, by 1931; as a type of score against one's own team, 1881.

Safety-valve, which diminishes the risk of explosion, is from 1797; figurative sense recorded from 1818. Safety-net in literal sense (in machinery) is by 1916, later of aerial circus performances (1920s); figurative use is by 1950. Safety-bicycle as a name for the modern type, with low, equal-sized wheels and a driving mechanism, is by 1866. Safety-razor is by 1877. A safety-belt (1840) was at first for window washers and firefighters; it was used of restraining straps for airplane pilots by 1911, extended to automobiles by 1948. Safety first as an accident-prevention slogan first recorded 1873.

Safety first, and saving of fuel second, should be the rule in steam engineering. [Scientific American, June 15, 1861]
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Newgate 

1596, in reference to the famous London prison, on the site of one of the seven gates in the old London wall (the main gate to the west); this one having been used as a lock-up since the 1100s. So called because it was thought to be more recent than the others (but it apparently dated to Roman times) or because it had been rebuilt at some point. The gate was demolished in the 18c.; the last prison of that name was torn down 1902-3.

Newgate frill, "a beard shaved so as to grow only under the chin and jaw," so called in allusion to the position of the hangman's noose, is by 1851. The author of "The Habits of Good Society" (1859) calls it "a kind of compromise between the beard and the razor."

Both Coleridge and Ruskin praised Thomas Hood's Newgatory.

Hood was addressing the admirable Mrs. Fry, who, as every one knows, set up a school in Newgate to teach the poor neglected outcasts what they had never heard from Christian lips before. One of the chief points made by Hood is this,—how much better, kinder, wiser, more politic even, it would be to multiply these schools outside, not inside the Prison walls, so that prevention might take the place of cure. [Alfred Ainger, preface to "Humorous Poems by Thomas Hood"]
As a literary study, this exquisite pun of Hood's ... deserves the most careful memory, as showing what a noble and instructive lesson even a pun may become, when it is deep in its purpose, and founded on a truth which is perfectly illustrated by the seeming equivocation. [Ruskin, "Fors Clavigera"]
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