The Proto-Indo-European word *dwoi-
Word *dwoi-
Meaning group of two, two
See also Old Norse: tveir ‘two’
Proto-Anatolian: *dwi ‘two’
Synonyms *dwéh₃(u)

Comments
Arm. erku/yerku/yergu, Alb. dy/dy, Lith. du/dvi, Ltv. divi, Gaul. vo, Gm. zwene/zwei, Eng. twā/two, Gk. duō, Av. duua, Hitt. dā-, Ir. dá/dó, Kashmiri zū', Lyc. tuwa, Kamviri dü, Lat. duo, Oscan dus, ON tveir, Old Prussian dwāi, Osset. dyuuæ/duuæ, Pers. duva/do, OCS dŭva, Polish dwa, Russ. dva, Skr. dva, Toch. wu/wi, Umbrian tuf, Goth. twai, Welsh dau

Other words that might be of interest
*hₓok̂tṓ(u) ‘eight’, *trei- ‘three’, *h₁oinos ‘one’, *kʷetwóres (m), kʷetwesóres (f), kʷetwōr (n) ‘four’, *(h₁)néwn̥ ‘nine’, *pénkʷe ‘five’, *sem- ‘one’, *septḿ̥ ‘seven’, *septm̥-k̂ómt-h₂ ‘seventy’, *kswek̂s ‘six’, *tréies (m), trisóres (f), treih₂ (n) tri- [prefix] ‘three’, *h₁newh₁m̥(h₁néwh₁n̥?) ‘nine’, *tóti ‘so much, many’, *tréyes ‘three’, *trī-k̂omt(hₐ) ‘thirty’, *kswek̂s-k̂omt(hₐ) ‘sixty’, *kʷetwóres ‘four’, *per(hₓ)- ‘first’, *dwiyos~dwitos ‘second’, *h₁newh₁m̥m/n̥-mos ‘ninth’, *hₓok̂towós ‘eighth’, *kswek̂sos ‘sixth’, *kʷturyós~kʷetwortos ‘fourth’, *pn̥kʷtós ‘fifth’, *septm̥-mós ‘seventh’, *triyós ‘third’