Dyo is the Greek cardinal numeral 'two,' appearing 137 times in the New Testament across every case and gender. It functions both as a simple quantifier — 'two brothers' (Matt 4:18), 'two sparrows' (Matt 10:29) — and as a theologically significant number: two witnesses establish testimony (Matt 18:16; Rev 11:3), two masters cannot both be served (Matt 6:24), and 'where two or three are gathered' Christ is present (Matt 18:20). The word is morphologically indeclinable in many contexts, as it was already in classical Attic. Spanish 'dos,' French 'deux,' and German 'zwei' all render it straightforwardly.