Iota is the smallest letter in the Greek alphabet, written as a single unadorned stroke, and that physical smallness gave rise to one of the most durable idioms drawn from any letter in this atlas: the Gospel of Matthew (5:18), in a passage about the permanence of religious law, states that not one iota or one stroke of a letter will pass from it, using the letter's minimal shape as a figure for the smallest conceivable unit of meaning; the English phrase not one iota, meaning not the slightest amount, descends directly from that verse.
In Byzantine Greek pronunciation, iota also became one of several vowels and vowel combinations that converged on the same simple i sound, a merger called iotacism, which is why several distinct ancient Greek vowels and diphthongs are all pronounced alike in modern Greek. Iota has only modest modern technical use, chiefly as a variable name in mathematics and programming where a short, unclaimed symbol is convenient, and astronomers, following the Bayer star-naming convention of 1603, use Iota to mark a constellation's ninth-brightest star. In the Milesian numeral system covered elsewhere in this atlas, iota carries the plain value of ten, one of the least remarked-upon assignments in that entire numbering scheme.