sibilant /ˈsɪb.ɪ.lənt/adjective 1noun 1forms 3 adjective1 •Characterized by a hissing or hushing sound such as the s or sh in sack or shack. noun1 •A consonant having a hissing or hushing sound such as the s or sh in sack or shack.Groove fricatives all have more or less of an [s]-like quality, and are for this reason sometimes called sibilants. — 1955 formssibilants · more sibilant · most sibilant