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.

late 14c., "direct, undeviating; not crooked, not bent or curved," of a person, "direct, honest;" properly "stretched," adjectival use of Old English streht (earlier streaht), past participle of streccan "to stretch" (see stretch (v.)). Related: Straightly; straightness.

Meaning "true, direct, honest" is from 1520s. Of communication, "clear, unambiguous," from 1862. Sense of "undiluted, uncompromising" (as in straight whiskey, 1874) is American English, first recorded 1856. As an adverb from c. 1300, "in a straight line, without swerving or deviating." Theatrical sense of "serious" (as opposed to popular or comic) is attested from 1895; vaudeville slang straight man first attested 1923.

Go straight in the underworld slang sense is from 1919; straighten up "become respectable" is from 1907. To play it straight is from 1906 in theater, 1907 in sports ("play fair"), with figurative extension; later perhaps also from jazz. Straight arrow "decent, conventional person" is 1969, from archetypal Native American brave name. Straight shooter is from 1928. Straight As "top grades" is from 1920.

"conventional," especially "heterosexual," 1941, a secondary sense evolved from straight (adj.1), probably suggested by straight and narrow path "course of conventional morality and law-abiding behavior," which is based on a misreading of Matthew vii.14 (where the gate is actually strait), and the other influence seems to be from strait-laced.

1640s, "a level position," from straight (adj.1). From 1864 as "straight part of a race track." Poker sense attested from 1841. Meaning "conventional person" is first recorded 1967, from straight (adj.2).

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]

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).

1938, of persons, "with visage showing no emotion or reaction," from expression keep a straight face (1897), from straight (adj.).

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.

1650s, "forming a straight line," with -ar + rectiline (1560s), from Late Latin rectilineus, from rectus "straight" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line") + linea "line" (see line (n.)). Of a figure, "bounded by straight lines," 1728. Related: Rectilineal "straight-lined" (1640s); rectilinearity.

"act of removing hair with a razor," also "thin slice taken off," late 14c., verbal noun from shave (v.). Shaving-cream is attested by 1851.