suffix forming almost all Modern English plural nouns, it was gradually extended in Middle English as -es from Old English -as. This was the nominative plural and accusative plural ending of certain "strong" masculine nouns, such as dæg "day," nominative/accusative plural dagas "days." In this use -s was the commonest Germanic declension, and traceable back to the original PIE inflection system. It is also the source of the Dutch -s plurals and (by rhotacism) Scandinavian -r plurals (such as Swedish dagar).

Modern English plural nouns have grown uniform. Old English also had a long list of "weak" nouns that formed their plurals in -an, as well as other strong nouns that formed plurals with -u. Quirk and Wrenn, in their Old English grammar, estimate that 45 percent of the nouns a student will encounter will be masculine, and of those nearly four-fifths will have nominative/accusative plural in -as. Less than half, but still the largest category.

The same Old English nouns also had genitive singular -es (see 's). The predominance of both -'s possessives and -s plurals in English is a common language pattern: a handful of suffixes are made to do multiple jobs (such as -ing), and the most common variant squeezes out the competition. To further muddy the waters, the use of -s has been extended in slang since 1936 to singulars (such as ducks, sweets, babes) as an affectionate or diminutive suffix.

Old English single-syllable collectives (sheep, folk) as well as weights, measures, and units of time did not use -s. The use of it in these cases began in Middle English, but the older custom is preserved in many traditional dialects (ten pound of butter; more than seven year ago; etc.).

third person singular present indicative suffix of verbs, it represents Old English -es, -as, which began to replace -eð in Northumbrian 10c., and gradually spread south until by Shakespeare's time it had emerged from colloquialism and -eth began to be limited to more dignified speeches.

snack treat, 1937, the plural of a childish contraction of some more, as in "Gimme some more of those." S'more as a contraction of some more is recorded by 1887.

"without date," an abbreviation of Latin sine anno "without a year," from sine "without" (see sans) + ablative of annus "year" (see annual (adj.)).

abbreviation of son of a bitch (q.v.). The existence of sob (n.) probably prevented it becoming a full acronym.

initialism (acronym) from shit out of luck (though sometimes euphemised), 1917, World War I military slang. "Applicable to everything from death to being late for mess" [Russell Lord, "Captain Boyd's Battery, A.E.F.," c. 1920]

the insignia of Rome, from Latin Senatus Populusque Romanus "the Senate and People of Rome."

1975 as an abbreviation of sexually transmitted disease, which is attested by 1918. Earlier it had been an abbreviation of Latin Sacrosanctae Theologiae Doctor "Doctor of Sacred Theology."

see sub voce.

also SWAT, 1968, acronym said to be for Special Weapons and Tactics squad or team; or Special Weapons Attack Team.