Borrowed from Latin Indus, from Ancient Greek Ἰνδός (Indós), from Old Persian 𐏃𐎡𐎯𐎢𐏁 (h-i-du-u-š /hiⁿduš/), from Proto-Iranian *hínduš (compare Avestan 𐬵𐬌𐬧𐬛𐬎 (hiṇdu)), from Proto-Indo-Iranian *síndʰuš or borrowed from Sanskrit सिन्धु (síndhu) (whence Sindh).
Another explication relates the origin of Indus to Indra which itself derives from the root indu, i.e. " water place or water spirit".