two

PIE word *dwóh₁ From Middle English two, twa, from Old English twā, feminine and neuter of twēġen (whence twain), from Proto-West Germanic *twai-, from Proto-Germanic *twai, from Proto-Indo-European *dwóh₁. Cognates Cognate with Scots twa (“two”); North Frisian tou, tuu (“two”); Saterland Frisian twäin, two (“two”); West Frisian twa (“two”); Dutch twee (“two”); Low German twee, twei (“two”); German zwei, zwo (“two”); Danish and Norwegian to (“two”); Swedish två, tu (“two”); Icelandic tvö (“two”); Faroese tvey (“two”); Latin duō (“two”); Ancient Greek δύο (dúo, “two”); Irish dhá (“two”); Lithuanian dù (“two”); Russian два (dva, “two”); Albanian dy (“two”); Old Armenian երկու (erku, “two”); Sanskrit द्व (dvá, “two”); Tocharian A wu, Tocharian B wi. Doublet of duo. See also twain. Unrelated to similar words in Austronesian languages such as Malagasy roa; Tagalog and Cebuano dalawa; West Coast Bajau and Minangkabau duo; Buginese ᨉᨘᨓ (dua); Indonesian, Malay, Iban, Iranun, Ilocano, and Sundanese dua; Fijian, Māori, Rapa Nui, and Rotuman rua; Tongan and Niuean ua; Wallisian, Samoan, and Hawaiian lua; and South Marquesan 'ua; which originated from Proto-Austronesian *duSa.

来源：wiktionary