deru-

Reconstructed with the dual meaning "tree, wood" and "firm, solid, true." Reflexes include Greek drŷ‍​‌​‌​‌​‍​‌​‌​‍​‌​‌​‌​‌​‍​‍​‍​‍​‌​‌​‌​‍​‌​‌​‌​‌​‌​‌​‌​‌​‍​‍​‌​‌s ("oak"), Latin dūrus ("hard"), Sanskrit dā́ru ("wood"), English tree and true, and Russian dérevo.

Discussion

The root *deru- is reconstructed with a primary meaning "tree, wood" and an extended sense "firm, so‍​‌​‌​‌​‍​‌​‌​‍​‌​‌​‌​‌​‍​‍​‍​‍​‌​‌​‌​‍​‌​‌​‌​‌​‌​‌​‌​‌​‍​‍​‌​‌lid, true," reflecting a semantic chain that proceeds from the material hardness of wood (especially oak) to abstract notions of reliability and truth. The root is treated in Pokorny (IEW 214–217), Watkins (s.v. deru-), and Mallory and Adams (1997). The dual semantic range — concrete and abstract — is confirmed by independent reflexes in multiple branches and is not a product of secondary contamination.

Greek drŷs (δρῦς, "tree, oak") preserves the arboreal meaning directly. The word referred specifically to the oak in classical usage, and the oak's association with Zeus at Dodona reflects the cultural significance of this tree in Greek religion. Latin dūrus ("hard, firm"), from the adjectival derivative *dr̥u-ro-, continues the abstract sense; its descendants include durable, duration, endure, and duress. The relationship between Greek drŷs ("oak") and Latin dūrus ("hard") illustrates the semantic bifurcation within the family: the concrete and abstract senses were already available in PIE and were distributed differently across branches.

Sanskrit dā́ru ("wood, timber") and the adjective dr̥ḍhá ("firm, fixed") attest both senses in Indo-Iranian. Avestan dāuru ("wood") confirms the Iranian cognate. The Celtic reflex appears in Old Irish daur ("oak") and in the widely discussed compound *dru-wid- ("tree-knower" or "strong seer"), conventionally regarded as the source of druí ("druid"), though the second element and the exact semantic interpretation remain debated. Thurneysen and later Delamarre have treated the Celtic evidence in detail.

The Germanic reflexes are of particular interest. English tree (from Old English trēow) and true (from Old English trēowe, "faithful, trustworthy") both descend from *deru-, preserving the concrete and abstract senses respectively within a single branch. The convergence of "tree" and "truth" in one etymon is not coincidental but reflects the deep metaphorical identification of firmness with trustworthiness: Proto-Germanic *trewwō ("faith, covenant") yields English truce, troth, and trust (through Old Norse). German Treue ("fidelity"), treu ("faithful"), and Baum (from a different root, which replaced *deru- in the arboreal sense) show the retention of the abstract meaning even after the loss of the concrete one.

Russian dérevo ("tree"), Lithuanian der̃va ("pinewood"), Old Church Slavonic drěvo ("tree"), and Albanian dru ("wood") extend the cognate set to the eastern branches. Beekes (s.v. δρῦς) accepts the reconstruction without reservation and notes the archaic character of the Greek form. The root provides a standard example in textbooks of how PIE vocabulary encodes the material culture of a society in which wood — particularly hardwood — served as the primary building material and the index of solidity.

Laryngeal Analysis

No laryngeal.

Ablaut

Full grade *deru-, zero grade *dru-, o-grade *doru-.