The Proto-Indo-European word *sem-
Word *sem-
Meaning one
See also Hittite: ša-ni-i ‘same, one and the same’
Hittite: ši-i- ‘one’
Avestan: hąm ‘together’
Synonyms *h₁oinos

Comments
Lat. semel, Arm. mi/mek/meg, Alb. gjithë, Lith. sa, Eng. sum/some, Gm. saman/zusammen, Gk. heis, Hitt. san, Av. hakeret, Ir. samail/samhail, Lyc. sñta, Kamviri sâ~, Pers. hama/hamin, Russ. sam, Skr. sakṛ t, Toch. sas/ṣ e, Welsh hafal, ON sami, Goth. sama

Other words that might be of interest
*hₓok̂tṓ(u) ‘eight’, *trei- ‘three’, *dwoi- ‘group of two, two’, *kʷetwóres (m), kʷetwesóres (f), kʷetwōr (n) ‘four’, *(h₁)néwn̥ ‘nine’, *pénkʷe ‘five’, *septḿ̥ ‘seven’, *septm̥-k̂ómt-h₂ ‘seventy’, *kswek̂s ‘six’, *tréies (m), trisóres (f), treih₂ (n) tri- [prefix] ‘three’, *dwéh₃(u) ‘two’, *h₁newh₁m̥(h₁néwh₁n̥?) ‘nine’, *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’