Origins
The word 'tree' descends from Old English 'trēow,' a word that in its earliest attestations carried a double meaning: both the living plant and, more abstractly, something firm, faithful, or true. This semantic duality — tree as both natural object and symbol of steadfastness — reaches back to Proto-Indo-European and illuminates a fundamental metaphor in the human understanding of the natural world.
Old English 'trēow' comes from Proto-Germanic *trewą, itself from PIE *drew- or the related nominal form *dóru, meaning 'wood,' 'tree,' or possibly 'oak' specifically. The PIE root is abundantly attested. Greek 'dóry' means a wooden spear shaft or beam (and gives 'Doric,' the austere architectural order, through association with the straight simplicity of wooden columns). Sanskrit 'dāru' means 'wood' or 'timber' (it survives in Hindi 'dar' and in 'deodar,' the divine cedar, literally 'wood of the gods'). Welsh 'derwen' means 'oak,' preserving what may have been the original specific reference. Russian 'derevo' (tree) and Lithuanian 'derva' (pinewood, resinous wood) continue the same root in the Balto-Slavic branch.
The connection between 'tree' and 'true' is one of the most celebrated semantic links in English etymology. Both words descend from the same Proto-Germanic root *treww-, which carried meanings spanning 'tree,' 'wood,' 'firm,' 'faithful,' and 'trustworthy.' Old English 'trēow' could mean 'tree' but also 'faith' or 'pledge' — a semantic range preserved in the archaic English phrase 'to plight one's troth' (pledge one's truth/faith) and in the word 'truce' (originally a pledge of faith). German preserves the split clearly: 'Baum' is tree, but 'Treue' (faithfulness, loyalty) and 'treu' (true, faithful) continue the abstract meaning of the same root. The metaphorical logic seems transparent: wood, especially oak, was the material emblem of solidity and dependability in a forested northern Europe.
Proto-Indo-European Roots
The word 'druid' has been connected to this root since antiquity. Pliny the Elder proposed that 'druid' derived from the Greek word for oak ('drys'), and modern scholars generally accept a Celtic compound of *dru- (strong, firm — or possibly 'oak,' from the same PIE root) and *wid- (to know), making a druid literally 'one with oak-knowledge' or 'one who knows firmly.' Whether the 'tree' element or the 'firm/strong' element is primary remains debated.
In Old English, 'trēow' was the general word for a tree, but the language also possessed a rich vocabulary of specific tree names, many of which have survived: 'āc' (oak), 'æsc' (ash), 'birce' (birch), 'elm,' 'lind' (linden), and many more. The compound 'trēowwyrhta' (tree-wright) meant a carpenter. The concept of a great cosmic tree — the World Tree — was central to Germanic mythology, known in Norse as Yggdrasil, the great ash that connected the nine worlds.
The phonological development from PIE *d to Germanic *t follows Grimm's Law perfectly (voiced stops become voiceless in Germanic), and the shift from *drew- to *trew- is entirely regular. The further development in English from Old English 'trēow' (two syllables, /treːow/) to Middle English 'tre' and then Modern English 'tree' involved the loss of the final syllable and the simplification of the diphthong.
Cultural Impact
The word 'tar' may also be related, deriving from Old English 'teoru,' from Proto-Germanic *terwą, from the same PIE root — tar being originally the resinous substance extracted from wood, especially pine. 'Trough' (Old English 'trog,' a vessel hollowed from a tree trunk) is another possible relative.
The importance of trees in Indo-European culture and religion is reflected in the vocabulary. Many European place-names derive from tree words: 'Derry' (from Irish 'doire,' oak grove), 'Lindau' (linden meadow), 'Birkenau' (birch meadow). The fact that a single PIE root could generate words for both the physical tree and the abstract concepts of truth, faith, and firmness suggests that for the earliest speakers of Indo-European languages, the tree was not merely a plant but a central symbol of the reliable, enduring structure of the world — a living pillar connecting earth and sky, its roots in the deep ground and its branches in the heavens.