deru- / Indo-European roots
Examples of words with the root deru-: betroth, dendro-, dendron, deodar, dour, druid, drupe, dryad, Dryopithecus, durain, duramen, duress, durum, endure, germander, hamadryad, indurate, obdurate, philodendron, rhododendron, shelter, tar, tray, tree, trig, trim, troth, trough, trow, truce.
To be firm, solid, steadfast; hence specialized senses "wood" "tree" and derivatives referring to objects made of wood.
▲ Derivatives include tree, trust, betroth, endure, druid.
1. Suffixed variant form *drew-o-.
a. tree from Old English trēow, tree, from Germanic *trewam;
b. truce from Old English trēow, pledge, from Germanic *treuwō.
2. Variant form dreu-.
a. true from Old English trēowe, firm, true;
b. trow from Old English trēowian, trūwian, to trust;
c. trig1 from Old Norse tryggr, firm, true;
d. troth, truth; betroth from Old English trēowth, faith, loyalty, truth, from Germanic abstract noun *treuwithō;
e. trust from Old Norse traust, confidence, firmness, from Germanic abstract noun *traustam;
f. tryst from Old French triste, waiting place (< "place where one waits trustingly"), probably from a source akin to Old Norse denominative treysta, to trust, make firm. a-f all from Germanic *treuwaz.
3. Variant form *drou-. tray from Old English trēg, trīg, wooden board, from Germanic *traujam.
4. Suffixed zero-grade form *dru-ko-.
a. trough from Old English trog, wooden vessel, tray;
b. trug from Old Norse trog, trough. Both a and b from Germanic *trugaz.
5. Suffixed zero-grade form *dru-mo-.
a. trim from Old English trum, firm, strong;
b. shelter from Old English truma, troop. Both a and b from Germanic *trum-.
6. Variant form *derw-. tar1 from Old English te(o)ru, resin, pitch (obtained from the pine tree), from Germanic *terw-.
7. Suffixed variant form *drū-ro-. dour, duramen, duress, durum; durain, dura mater, endure, indurate, obdurate from Latin dūrus, hard (many of whose English derivatives represent a semantic cross with Latin dūrāre, to last long; see deuə-)
8. Lengthened zero-grade form *drū-. drupe, dryad; Dryopithecus, germander, hamadryad from Greek drūs, oak.
9. Reduplicated form *der-drew-, dissimilated with suffix in *der-drew-on. dendro-, dendron; philodendron, rhododendron from Greek dendron, tree.
10. druid from Latin druides, druids, probably from Celtic compound *dru-wid-, "strong seer" (*wid-, seeing; see weid-) , the Celtic priestly caste.
11. O-grade form *doru-. deodar from Sanskrit dāru, wood, timber.
[Pokorny deru- 214.]