sib·i·lant (sĭb'ə-lənt) adj. Of, characterized by, or producing a hissing sound like that of (s) or (sh): the sibilant consonants; a sibilant bird call. n. A sibilant speech sound, such as English (s), (sh), (z), or (zh).
[Latin sībilāns, sībilant-, present participle of sībilāre, to hiss.] sib'i·lance, sib'i·lan·cy n., sib'i·lant·ly adv.
1669, from L. sibilantem (nom. sibilans), prp. of sibilare "to hiss, whistle," possibly of imitative origin (cf. Gk. sizein "to hiss," Lett. sikt "to hiss," O.C.S. svistati "to hiss, whistle"). The noun meaning "speech sound having a hissing effect" is from 1788.