straight | Etymology of straight by etymonline

early 14c., streight, of the body, "not bent or curved, not bent," like a string stretched tight or drawn out, etymologically, "stretched" (a sense once current but now obsolete); from adjectival use of Old English streht (earlier streaht), past participle of streccan "to stretch" (see stretch (v.)). Related: Straightly; straightness.

By late 14c. of a line, street, etc., "direct, undeviating;" by early 15c. of a person, "direct, honest;" of conduct, "free from crookedness," 1520s.

Of communication, "clear, unreserved, unambiguous," by 1862. The sense of "undiluted, unmixed, pure" (as in straight whiskey, 1874) is American English, attested by 1856. The meaning "continuous, unbroken" (six straight days) is by 1899; compare use of the noun in poker (1841). The theatrical sense of "serious" (as opposed to popular or comic) is attested by 1895; vaudeville slang straight man for one of a comedy duo is attested by 1906.

Straight arrow "decent, conventional person" is 1969, from a stereotypical Native American brave name. Straight shooter "honest person" is from 1892. Straight As "top grades" is from 1920. Straight-razor is by 1908, after other sorts had come along.

For "not homosexual," see straight (adj.2).

"conventional," especially "heterosexual," 1941, a secondary sense evolved from straight (adj.1) in one of its senses, probably suggested by the stock phrase straight and narrow path or way, "course of conventional morality and law-abiding behavior" (by 1842), which is based on a misreading of Matthew vii.14 (where the gate is actually strait); another influence seems to be strait-laced.

1640s, "a level position," from straight (adj.1). From 1864 as "straight part of a race track." Poker sense of "a sequence of cards," generally five of them, is attested from 1841. However straight poker (1864) is "the game in its unmodified form." The meaning "conventional person" is recorded by 1967, from straight (adj.2).

c. 1300, "in a straight line, without swerving or deviating;" also "at once, immediately, directly;" from straight (adj.1).

To think straight "think clearly" is by 1916. To go straight in the underworld slang sense of "give up a life of crime" is from 1919 (straighten up "become respectable" is from 1907). To play it straight is from 1906 in theater, by 1907 in sports ("play fair"), and with later figurative extension some of them perhaps from jazz slang use. To do something straight off "without delay" is by 1873.