sibilate
verb
sib·i·late ˈsi-bə-ˌlāt 
sibilated; sibilating
intransitive verb
1
: hiss
2
: to utter an initial sibilant : prefix an \\s\\-sound
transitive verb
1
: hiss
2
: to pronounce with an initial sibilant : prefix an \\s\\-sound to
sibilation
ˌsi-bə-ˈlā-shən
noun 
Word History
Etymology
Latin sibilatus, past participle of sibilare
First Known Use
circa 1656, in the meaning defined at intransitive sense 1