sibilant vs assibilate

sibilant is a noun but assibilate is not a noun.

Word	Noun	Adjective	Verb	Adverb
sibilant	Yes	Yes	No	No
assibilate	No	No	Yes	No

sibilant (noun)	assibilate (noun)
a consonant characterized by a hissing sound (like s or sh)

sibilant (adjective)	assibilate (adjective)
of speech sounds produced by forcing air through a constricted passage (as `f', `s', `z', or `th' in both `thin' and `then')

sibilant (verb)	assibilate (verb)
	change into a sibilant
	insert a sibilant sound before or after (another sound)