-s

¹-s

noun pl suffix
\s after a voiceless consonant, z after a voiced consonant or a vowel\

Definition of -S

—used to form the plural of most nouns that do not end in s, z, sh, ch, or postconsonantal y <heads> <books> <boys> <beliefs>, to form the plural of proper nouns that end in postconsonantal y <Marys>, and with or without a preceding apostrophe to form the plural of abbreviations, numbers, letters, and symbols used as nouns <MCs> <PhD's> <4s> <the 1940's> <$s> <B's> — compare ¹-es

Origin of -S

Middle English -es, -s, from Old English -as, nominative & accusative plural ending of some masculine nouns; akin to Old Saxon -os