S, 19th letter of the English alphabet. It first appeared in its modern form in the Roman alphabet, as the equivalent of the Greek letter sigma, ultimately derived from an Egyptian hieratic character based on the hieroglyph for an inundated garden.

The s sound, technically known as a sibilant consonant, may be either voiceless or voiced. The letter s is occasionally given the phonetic value of sh or zh in words such as sure and treasure; it is silent in a few words, including aisle and debris.