insert a sibilant sound before or after (another sound)
<verb.communication>
change into a sibilant
<verb.change> In the syllable /si/, the /s/ sibilates in Japanese
Assibilate \As*sib"i*late\, v. t. [L. assibilatus, p. p. of assibilare to hiss out; ad + sibilare to hiss.] To make sibilant; to change to a sibilant. --J. Peile.