A line that does not bend
In present-day English, straight names a body, a road, a strand of hair, or an argument that holds one direction. The same form also covers an honest deal, a run of consecutive wins, liquor poured without a mixer, and, in later slang, a conventional or heterosexual person. The cluster looks miscellaneous until the older physical picture is recovered: something pulled taut until it no longer kinks.
A native participle, not a loan
The origin of the word straight is home-grown. English did not borrow this adjective from French or Latin. It is the old past participle of the verb that became modern stretch, put to work as a describing word.
In Old English that verb was streccan, with a past participle streaht, later simplified to streht. Middle English kept the participle in spellings such as streight, streght, and streiȝt, beside the related verb strecchen. Historical dictionaries treat the modern adjective as that participle converted into an independent word. The earliest evidence is sometimes placed around 1225, in the Middle English legend of St. Margaret, where a related form still means a hand stretched out. The familiar sense of a body that is not bent or curved is firmly in place by the early fourteenth century, often under the spelling streight.
The gh in the modern spelling is a fossil of that participle, not an ornamental extra. The same history yields an older doublet, straught, which survives in dialect and in older texts. Morphologically the adjective is stretch plus the old weak-verb ending, frozen so thoroughly that speakers no longer hear it as a verb form.
As an adverb the word is already in use around 1300, both for motion that does not swerve and for doing something at once. That second use, still alive when someone goes straight home, takes the unbent path and applies it to time.
West Germanic stretch, a hazier root beyond
The Old English verb comes from Proto-West Germanic strakkjan, a causative built on an adjective strak meaning stretched or taut: to stretch is, at that stage, to make something straight. Related verbs remain obvious across the family. German has strecken, Dutch strekken, Danish strække, Swedish sträcka, West Frisian strekke. Past-participial adjectives in those languages still mean stretched: German gestreckt, Dutch gestrekt, Danish strakt. Scots keeps straicht beside the southern English form.
How far the chain goes beyond Germanic is less settled. Some accounts link the family to the same stock as stark, with a sense of stiffness. Others point to a reconstructed Indo-European root of the strenk type, the one that also feeds English string, with a meaning of pulling tight. Reconstructions sometimes give streg or treg for stiff or rigid. None of these deeper ties is as secure as the West Germanic verb. The honest stopping place is tautness and stretch, not a single agreed prehistoric syllable.
From taut body to honest person
Once the participle meant stretched out, not flexed, later senses are a series of metaphors that keep the idea of no deviation.
By the late fourteenth century the word described a line, street, or course that did not swerve. Early in the fifteenth century it could describe a person as direct; by the 1520s, conduct as free of crookedness. The moral use is still spatial: a crooked deal is one that bends. Communication that is clear and unreserved is recorded in the nineteenth century. American English added the liquor sense, unmixed, by the 1850s. Consecutive, unbroken time — six straight days — belongs to the late nineteenth century, overlapping the poker noun for a run of cards in sequence, attested from 1841.
The noun for a level stretch of ground is seventeenth century; the unbent part of a racetrack is mid-nineteenth. Theatre borrowed the adjective for serious as opposed to comic by the 1890s, and the vaudeville straight man follows in the early twentieth. Underworld slang for leaving crime is recorded after the First World War.
A later layer, conventional and then specifically heterosexual, is dated to 1941. Sources treat it as a development of the older moral and spatial senses, helped along by the stock phrase about the straight and narrow path. That phrase itself rests on a mix-up. The Gospel verse behind it, in older English Bibles, speaks of a strait gate: narrow, from Latin strictus through Old French estreit, the ancestor of modern French étroit. English straight, Germanic and related to stretch, and English strait, Romance and related to strict, have been homophones for centuries and have borrowed each other’s spellings. Some later senses of straight have been pulled toward the Romance word. They are not the same etymon, even when they sound identical.
What the participle still shows
If one fact organizes the whole vocabulary, it is this: the adjective began as stretched, the completed action of Old English streccan, and English never needed to import a new root in order to talk about lines, honesty, or an unmixed drink. The lookalike strait is the one that came in from Latin. Keep those two histories apart and the later slang, the poker hand, and the racetrack all sit on the same taut line.