What the adjective does now
In present-day English, trustworthy names a person, a source, or an object that deserves confidence. A babysitter, a dataset, a newspaper, and a lock can all take the word. The judgment is practical rather than ceremonial: if you rely on this thing, you are not being reckless. Legal English sometimes narrows the same idea to a source fit to be believed as evidence. The everyday sense has not needed much renovation. Unlike many moral adjectives that drifted from piety into mere politeness, this one still does the job it was built for.
Built in English from two older pieces
The origin of the word trustworthy is not a foreign import taken over as a finished unit. Historical dictionaries treat it as a compound formed inside English from the noun trust and the adjective worthy, or from the combining form -worthy that had already been productive for centuries. The pattern is the same one behind seaworthy, blameworthy, and later creditworthy: a familiar stem plus a second element that means deserving of, fit for, or able to bear. The Oxford English Dictionary compares an earlier parallel, faithworthy, assembled on the same plan. A speaker who knows the parts can still hear the whole without a glossary.
The first half: trust, and a live argument about its path
The noun is the historically noisy piece. Middle English trust and trost, in the sense of confidence, protection, and reliance, are on record from about 1200. Popular etymologies still repeat the older handbook story: a borrowing from Old Norse traust, help, confidence, protection. That account is not empty. Norse and English were in close contact, and the Scandinavian word sits in the right semantic neighborhood.
Recent treatments, including the English Wiktionary entry, flag a problem of vocalism. Old Norse traust does not line up cleanly with the English vowel. One alternative is an unattested Old English form of the same family, a rare zero-grade variant of the Proto-Germanic root, with a possible continental cousin in Middle High German getrüste, a host or company. The point is unsettled. What is not unsettled is the deeper layer. Either route leads to Proto-Germanic *traustą, an abstract noun in the same cluster as *treuwaz, faithful. English already had that second branch natively: Old English treowe and triewe, the ancestor of true, and the verb treowian, to believe or trust.
The usual reconstruction takes the cluster back to a Proto-Indo-European root *deru-, firm, solid, steadfast, the same stock that yields tree. Firmness and fidelity were bound in the root rather than pasted on later as a metaphor. Germanic relatives keep both faces of the idea. Icelandic still has traust for faith and confidence. German Trost and Dutch troost shifted toward comfort and consolation. Gothic trausti meant an agreement or alliance. On the true side sit German treu, Dutch getrouw, Old Norse tryggr, and Gothic triggws.
Later senses of the English noun sit beside the adjective rather than underneath it. The legal trust, property held for another, is a fifteenth-century development. The American industrial trust, a combination of companies under one control, is nineteenth-century. Trustworthy never meant a cartel. It rates fitness to receive confidence.
The second half: worthy and a busy suffix
Worthy is native. Middle English worthy, also spelled wurthi, is worth plus the adjective-forming suffix later written -y, matching an Old English type *weorþiġ. Close cousins are easy to point to: Dutch waardig, German würdig, Swedish värdig. From the thirteenth century the combining form -worthy was already at work in compounds, sometimes in the sense of sufficient importance, sometimes of fitness to endure. In this adjective it carries the first of those jobs more than the second: able to be trusted, fit to receive trust, not able to survive a storm.
Proto-Germanic *wirþijaz, worthy, is usually taken from a root *wert-, to turn, the family behind worth, German werden, and Latin vertere. That is a different Indo-European line from the tree-and-true root in trust. The compound therefore joins two Germanic inheritances, not two halves of one ancient word.
Why the first dates refuse to agree
Dictionaries still print different first English dates, and the spread is wide enough to mention. The current Oxford English Dictionary places the earliest evidence in 1658, in the writing of E. Hyde. Merriam-Webster now gives the same year. Older reference works sat much later. Etymonline still prints 1791. Dictionary.com still gives 1800 to 1810. The 1989 OED began at 1808. Some earlier Merriam-Webster printings used 1714. Other reports identify the 1658 source as Edward Hyde, Christ and his Church. The disagreement is not about meaning. It is about which quotations had been found when each work went to press. A revised historical dictionary pushed the record back into the mid-seventeenth century.
Derived forms trail the adjective at different distances. The OED has the noun trustworthiness from 1662. Shorter dictionaries place the adverb trustworthily in the mid-nineteenth century. Untrustworthy is later still; a survey of OED citations points to 1846 in Joseph Emerson Worcester's dictionary. From the first securely dated uses, the adjective already means deserving of trust or confidence. There is no obsolete sense that a modern reader has to unlearn.
What English said before it had this compound
The language was not waiting for a missing idea. Trusty is older by centuries: early thirteenth century from trust plus -y, first in the sense of trusting, a meaning now gone, then by the early fourteenth century reliable and loyal. Old English had already used treowful and the everyday adjective treowe for the same moral ground. True itself, before it specialized toward correspondence with fact, meant faithful and steady in promises. The seventeenth-century compound did not fill a vacuum. It offered a more explicit, two-part rating at a moment when -worthy formations were a familiar way to make that rating audible.
A useful leftover is the family resemblance hiding in plain sight. The person you call trustworthy sits on the same old root as true, and more distantly as tree: something that holds and does not give way. The adjective itself is not ancient. It is an English build of the 1600s. What is ancient is the idea it names, and the Germanic stock that already linked firmness with faith.