[sib.i.lant] adj [L sibilant-, sibilans, prp. of sibilare to hiss, whistle, of imit. origin] (1669): having, containing, or producing the sound of or a sound resembling that of the s or the sh in sash "a ~ affricate" "a ~ snake" -- sib.i.lant.ly adv
[2]sibilant n (1788): a sibilant speech sound (as English /s/, /z/, /sh/, /zh/, /ch( tsh)/, or /j( dzh)/)