S, the nineteenth letter and chief sibilant of the English alphabet. The sound of it is formed by forcing the breath through a narrow passage between the palate and the tongue elevated near it, together with a motion of the lower jaw and teeth, towards the upper jaw. Its sound, however, varies, being strong in some words, as this, thus, and soft in words which have a final e, as muse, wise (pronounced z). It is generally doubled at the end of words, by which they become hard and harsh, as in kiss, loss. In some words it is silent, as isle, island, viscount. It is subject to numerous interchanges, which are observable in most languages. The following are the best known:—S interchanges with d, th, t, z, sh, c, g, h, ks, with g, n, and r. The letter S is frequently dropped, of which we have numerous examples in the history of the French language.
In abbreviation, S. stands for societas or socius; as R.S.S. for regia societatis socius, fellow of the royal society. In medicinal prescriptions, S.A. signifies secundum artem, according to the rules of art. And in the notes of the ancients, S. stands for Sextus; S.P. for Spurius; S.C. for senatus consultum; S.P.Q.R. for senatus populusque Romanus; S.S.S. for stratum superstratum, one layer above another alternately; S.V.B.E.Q.V. for si vales bene est, ego quoque valeo, a form used in Cicero's time in the beginning of letters. (See ABBREVIATIONS.) Used as a numeral, S. anciently denoted seven; in the Italian music, S. signifies solo; and in books of navigation, S. stands for south, S.E. for south-east, S.W. for south-west, S.S.E. for south-south-east, S.S.W. for south-south-west.