suffix forming almost all Modern English plural nouns, gradually extended in Middle English from Old English

-as

, the nominative plural and accusative plural ending of certain "strong" masculine nouns (such as

dæg

"day," nominative/accusative plural

dagas

"days"). The commonest Germanic declension, 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

).Much more uniform today than originally; Old English also had a numerous category of "weak" nouns that formed their plurals in

-an

, and 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, nearly four-fifths of them with genitive singular

-es

and nominative/accusative plural in

-as

. Less than half, but still the largest chunk.The triumphs of

-'s

possessives and

-s

plurals represent common patterns in language: using only a handful of suffixes to do many jobs (such as

-ing

), and the most common variant squeezing out the competition. To further muddy the waters, it's 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.).