sib·i·lant [ˈsibələnt] adj. Of, characterized by, or producing a hissing sound like that of (s) or (sh).
Etymology: 1660s, from Latin sibilantem (nominative sibilans), present participle of sibilare "to hiss, whistle," possibly of imitative origin (cf. Greek sizein "to hiss," Lettish sikt "to hiss," Old Church Slavonic svistati "to hiss, whistle"). The noun meaning "speech sound having a hissing effect" is from 1788.