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"). Related: Sibilance; sibilation (1620s).
"speech sound having a hissing effect," 1772, from sibilant (adj.).
sibilant sib·i·lant (sĭb'ə-lənt)
Of, characterized by, or producing a hissing sound like that of (s) or (sh).