iota |īˈōtə| noun 1 the ninth letter of the Greek alphabet ( Ι, ι), transliterated as ‘i.’ • ( Iota) [followed by Latin genitive] Astronomy the ninth star in a constellation : Iota Piscium. 2 [in sing. ] [usu. with negative ] an extremely small amount : nothing she said seemed to make an iota of difference. [ORIGIN: iota being the smallest letter of the Greek alphabet. Compare with...