Loyalty before fact
In modern English, true is first of all the opposite of false. A claim is true when it matches the world. The same adjective still means loyal, as in a true friend; genuine, as in true gold rather than a fake; and accurately aligned, as in a wheel that is true or a bearing of true north. Those uses look scattered until you see the older centre of the word: something that holds firm and can be relied on. The origin of the word true is a story about faithfulness that later absorbed the job of matching facts.
Inherited, not borrowed
English did not take this adjective from French or from Latin. It is native. Middle English wrote trewe, treu, treowe, and later true, from Old English triewe in the West Saxon dialect and treowe in Mercian. The word is already there in the Old English period, before 1150. Its early meaning was faithful, trustworthy, honest, and steady in keeping promises or standing by friends.
Some historical dictionaries add a second, smaller path: a few early instances look like a shortened form of the prefixed Old English adjective i-treowe, which is more common in the surviving texts. That does not change the larger picture. The word is Germanic. Latin verus, the usual classical word for what is factually so, gave English a different set: very, verity, verify. True and very are not relatives, even if they now overlap in meaning.
Germanic cognates still lean toward loyalty. German treu and Dutch trouw mean loyal. Gothic triggws meant faithful. Old Norse tryggr meant firm and trustworthy; Danish and Swedish trygg have moved toward safe and secure. Old Frisian had triuwi. Across the family, the first picture is a person, a pledge, or a bond you can count on.
A root shared with tree
Handbooks reconstruct a Proto-Germanic adjective, treuwaz in some accounts and triwwiz in others, with the sense of having good faith. Behind it they place a Proto-Indo-European root written deru, dreu, or drewH, meaning firm, solid, steadfast. That root also specialized toward wood and trees. In Old English the noun treow, tree, and the adjective treowe, faithful, still looked and sounded closer than modern tree and true.
The link is a reconstruction. It is widely accepted, but it is not a documented medieval explanation, and some accounts mark it as probable rather than certain. The semantic step is straightforward: timber stands fast, so words for wood can shade into words for reliability. A useful parallel, not a borrowing, is Latin robustus, tough, from robur, the red oak. Celtic neighbours sit nearby: Old Irish derb, sure, and Welsh derw, which can mean true, beside words for oak. Lithuanian drutas means firm. Sanskrit daru is wood. Greek drys is oak.
English built a cluster on the same Germanic stem. Truth, and the older form troth, come from Old English treowth: good faith, honour, fidelity, a covenant. The noun is the adjective plus a suffix. Truce comes from a related noun treow, a pledge or compact. Trow, now rare, was the verb to trust or believe. Trust is usually explained through Old Norse traust, help and confidence, from an ablaut variant of the same base. Betroth belongs here as well. None of this is prefix-and-root analysis of the modern spelling; it is one inherited stem branching into noun, verb, and later compounds.
How the meaning moved
The sense that now feels primary, consistent with fact, is historically later. It is recorded from about 1200. Old English already had some uses touching veracity, but the ordinary word for factual truth was soth, later sooth. Reconstruction of Proto-Germanic makes the same point: the treuwaz family was not the usual word for correct as opposed to wrong; that work belonged to a different stem, santhaz, which survives as Swedish sann and Danish sand, and in English only as faded sooth.
English therefore shifted a loyalty word onto propositions. Late in the fourteenth century the adjective also meant real or genuine, not counterfeit. Around 1400 it could mark legal right, as in a true heir. By the 1540s it meant exact against a standard, including true north. Late fifteenth-century English applied it to objects accurately fitted or shaped. From that mechanical sense, nineteenth-century workmen made a verb: to true a part is to bring it into alignment. An older verb sense, to verify, from the 1640s, dropped out.
Pieces of the old social meaning remain. A true friend is loyal first. Come true, of dreams, is attested from 1819: a hoped-for picture lining up with events. True-born dates from the 1590s. The Boolean value in logic and computing is a late specialization of the factual sense, not a new history.
Sooth itself left ordinary speech after the mid-seventeenth century, surviving in forsooth and in later archaizing style. English kept the faithfulness word and stretched it until it covered what sooth had done.
What Danish still shows
Danish tryg no longer means true in the English sense. It means safe. That shift keeps the original Germanic centre in view: not a sentence that matches a fact, but a bond that does not give way. English moved the same stem onto statements, copies, compass bearings, and wheels. The older social meaning did not vanish; it simply stopped being the main work of the word.