assibilate vs sibilant

assibilate is not a noun while sibilant is a noun.

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

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

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

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