n. Change of a non-sibilant letter to a sibilant, as of -tion to -shun, duke to ditch. [ 1913 Webster ]
n. [ L. sibilatio. ] Utterance with a hissing sound; also, the sound itself; a hiss. [ 1913 Webster ]
He, with a long, low sibilation, stared. Tennyson. [ 1913 Webster ]