From Proto-Tai *siːᴮ (“four”), from Middle Chinese 四 (MC siɪH, “four”), from Proto-Sino-Tibetan *b-ləj (“four”). Cognate with Thai สี่ (sìi), Northern Thai ᩈᩦ᩵, Lao ສີ່ (sī), Lü ᦉᦲᧈ (ṡii1), Tai Dam ꪎꪲ꪿, Shan သီႇ (sìi), Ahom 𑜏𑜣 (sii), Zhuang seiq.
ᥔᥤᥱ (si3) (old orthography ᥔᥤˇ)