also *dreu-, Proto-Indo-European root meaning "be firm, solid, steadfast," with specialized senses "wood," "tree" and derivatives referring to objects made of wood.
It forms all or part of: betroth; Dante; dendrite; dendro-; dendrochronology; dour; Druid; drupe; dryad; dura mater; durable; durance; duration; duress; during; durum; endure; hamadryad; indurate; obdurate; perdurable; philodendron; rhododendron; shelter; tar (n.1) "viscous liquid;" tray; tree; trig (adj.) "smart, trim;" trim; troth; trough; trow; truce; true; trust; truth; tryst.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dru "tree, wood," daru "wood, log, timber;" Greek drys "oak," drymos "copse, thicket," doru "beam, shaft of a spear;" Old Church Slavonic drievo "tree, wood," Serbian drvo "tree," drva "wood," Russian drevo "tree, wood," Czech drva, Polish drwa "wood;" Lithuanian drūtas "firm," derva "pine, wood;" Welsh drud, Old Irish dron "strong," Welsh derw "true," Old Irish derb "sure," Old Irish daur, Welsh derwen "oak;" Albanian drusk "oak;" Old English treo, treow "tree," triewe "faithful, trustworthy, honest."
"betroth (two people), bind in wedlock; pledge oneself to," early 12c., from Old English handfæsten and cognate Old Norse handfesta "to pledge, betroth; strike a bargain by shaking hands;" for first element see hand (n.); second element is from Proto-Germanic causative verb *fastjan "to make firm," from PIE *past- "solid, firm" (see fast (adj.)). Related: Handfasted; handfasting. The noun in Old English was handfæstung.
Old English weddian "to pledge oneself, covenant to do something, vow; betroth, marry," also "unite (two other people) in a marriage, conduct the marriage ceremony," from Proto-Germanic *wadja (source also of Old Norse veðja, Danish vedde "to bet, wager," Old Frisian weddia "to promise," Gothic ga-wadjon "to betroth"), from PIE root *wadh- (1) "to pledge, to redeem a pledge" (source also of Latin vas, genitive vadis "bail, security," Lithuanian vaduoti "to redeem a pledge"), which is of uncertain origin.
The sense has remained closer to "pledge" in other Germanic languages (such as German Wette "a bet, wager"); development to "marry" is unique to English. "Originally 'make a woman one's wife by giving a pledge or earnest money', then used of either party" [Buck]. Passively, of two people, "to be joined as husband and wife," from c. 1200. Related: Wedded; wedding.