deru-

The semantic development of *deru- ranks among the most instructive in Indo-European linguistics. The progression from "tree" to "wood" to "firm, solid" to "true, trustworthy" traces a metaphorical chain rooted in the material properties of wood: that which is firm as oak is reliable, and that which is reliable is true. Latin dūrus ("hard, firm") continues the adjectival sense. From dūrus derive durable, duration, endure, during, and duress. The noun rōbur ("oak, hardwood, strength") — from a variant formation — gives robust and corroborate. Greek drŷs (δρῦς, "tree, oak") preserves the arboreal meaning. The druid tradition (attested in Celtic) appears to contain this root: Old Irish druí ("druid") is conventionally analysed as *dru-wid-, "tree-knower" or "strong seer," combining *deru- with *weyd- ("to know"). The Dryads (Dryádes, "tree nymphs") of Greek mythology derive from drŷs. Sanskrit dā́ru ("wood, timber") and the adjective dr̥ḍhá ("firm, fixed") show both the material and abstract senses. The Avestan cognate dāuru ("wood") confirms the Indo-Iranian reconstruction. In Germanic, English tree (from Old English trēow, which also meant "truth, pledge") and true (from Old English trēowe, "faithful, trustworthy") descend from this root. The convergence of "tree" and "true" in the same etymon is not a coincidence but reflects the deep semantic network: a true person is firm as a tree; a troth ("pledge") is given under an oak. German Treue ("loyalty, fidelity"), treu ("faithful"), and Baum (from a different root for "tree," which replaced the inherited *deru- form in the arboreal sense) show the survival of the abstract meaning even after the concrete meaning was lost. Russian dérevo ("tree") and Lithuanian der̃va ("pinewood") preserve the Balto-Slavic reflexes. The Albanian dru ("wood") and Old Church Slavonic drěvo ("tree") complete the picture.