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Webster 1913 Edition
Sibilation
Sibˊi-la′tion
,Noun.
 [L. 
sibilatio
.] Utterance with a hissing sound; also, the sound itself; a hiss. 
He, with a long, low 
sibilation
, stared. Tennyson.
Webster 1828 Edition
Sibilation
SIBILA'TION
,Noun.
  Definition 2025
sibilation
sibilation
English
Noun
sibilation (plural sibilations)
-  A hissing sound.
- From the shadows emanated a hushed sibilation.