Not just “word” — the claim that the world is something reason can actually get a grip on.
English inherits logos mostly as invisible scaffolding — buried in “biology,” “psychology,” “epistemology” — without carrying over what the word originally staked a claim about. Before it meant “the study of,” it meant something closer to “the rational order a thing can be given an account of.”
Heraclitus, in the 6th century BC, was the first philosopher to make logos a technical term: the common rational structure underlying a constantly changing cosmos, which most people live “as if asleep” to, failing to notice even though it’s “common to all.” The Stoics later extended this into a cosmic governing principle (logos spermatikos), and the term migrated into rhetoric (Aristotle’s appeal to reasoned argument, one of his three pillars of persuasion alongside ethos and pathos) and later Christian theology (the Gospel of John’s opening line). All these senses share Heraclitus’s original wager: that reality is structured in a way reasoned discourse can actually track, not merely describe from outside.
Source: Johnstone, M.A. (2014). “On ‘Logos’ in Heraclitus.” Oxford Studies in Ancient Philosophy, 47, 1–30. See also Hussey, E. (1982). “Epistemology and Meaning in Heraclitus,” in Language and Logos (Cambridge University Press).