dwo- / Indo-European roots
Examples of words with the root dwo-: anadiplosis, balance, barouche, between, betwixt, bezel, bi-, binal, binary, bis, bis-, biscuit, combine, conduplicate, deuce, Dhivehi, di-, dichasium, dicho-, didymium, didymous, diplo-, diploe, diploid, diploma, dodecagon, double, doubloon, doubt, dozen.
▲ Derivatives include twilight, biscuit, between, combine, diploma, doubt.
I. Variant form *duwo.
1. a. two from Old English twā̆, two (nominative feminine and neuter); b. twain; twayblade from Old English twēgen, two (nominative and accusative masculine). Both a and b from Germanic *twa, two.
2. twelfth, twelve from Old English twelf, twelve, and twelfta, twelfth, from Germanic compound *twa-lif-, "two left (over from ten)" twelve (*-lif-, left; see leikw-)
II. Adverbial form *dwis and combining form *dwi-.
1. a. twilight from Old English twi-, two; b. zwieback, zwitterion from Old High German zwi-, twice. Both a and b from Germanic *twi-.
2. bi-1, bis, bis-; balance, barouche, bezel, biscuit, bistort from Latin bis (combining form bi-), twice.
3. di-1 from Greek dis (combining form di-), twice.
4. twist from Old English -twist, divided object, fork, rope, from Germanic *twis.
5. twice from Old English twige, twiga, twice, from Germanic *twiyes.
6. twenty from Old English twēntig, twenty, from Germanic compound *twēgentig, "twice ten" (*-tig, ten; see dekm̥)
7. twine from Old English twīn, double thread, from Germanic *twīhna, double thread, twisted thread.
8. between, betwixt, twixt from Old English betwēonum and betweox, betwix, between, from Germanic compounds *bi-twīhna and *bi-twisk, "at the middle point of two" (bi, at, by; see ambhi)
9. twill from Old English twilic, woven of double thread, from Germanic compound *twilic-, "two-threaded fabric"
10. Suffixed form *dwis-no-. a. twin from Old English twinn, getwinn, two by two, twin, from Germanic *twisnaz, double; b. bi-1, binal, binary; combine, pinochle from Latin bīnī, two by two, two each.
11. Suffixed form *dwi-ko-. twig1 from Old English twigge, a branch, from Germanic *twig(g)a, a fork.
12. Compound *dwi-plo-, twofold (*-plo-,-fold; see pel-2) diplo-, diploe, diploid, diploma; anadiplosis, diplodocus from Greek diploos, diplous, twofold.
13. Suffixed reduplicated form *dwi-du-mo-. didymium, didymous; epididymis from Greek didumos, double, the testicles.
14. Suffixed form *dwi-gha. dichasium, dicho- from Greek dikha, in two.
15. Dhivehi from Sanskrit dvīpaḥ, island, from earlier *dvi-əp-o- "having water on two sides" (*ap-, əp-, water).
III. Inflected form *duwō.
1. deuce1, dozen, dual, duet, duo, duo-; duodecimal, duumvir from Latin duo, two.
2. duad, dyad; dodecagon, hendiadys from Greek duo, duō, two.
IV. Variant form *du-.
1. Compound *du-plo-, twofold (*-plo-,-fold; see pel-2) double, doublet, doubloon, duple from Latin duplus, double.
2. Compound *du-plek-, twofold (*-plek-,-fold; see plek-) duplex, duplicate, duplicity; conduplicate from Latin duplex, double.
3. Suffixed form *du-bhw-io-. doubt, dubious; redoubtable from Latin dubius, doubtful (< "hesitating between two alternatives"), and dubitāre, to be in doubt.
V. Also ultimately from this root, although the exact preform is unclear, is the Middle Indic prefix *du-, two. dupatta
[Pokorny du̯ō(u) 228.]