-s \-s\ 1. [OE. es, AS. as.] The suffix used to form the plural of most words; as in roads, elfs, sides, accounts. 2. [OE. -s, for older -th, AS. -[eth].] The suffix used to form the third person singular indicative of English verbs; as in falls, tells, sends. 3. An adverbial suffix; as in towards, needs, always, -- originally the genitive, possesive, ending. See {-'s}.