sibilant vs sibilate

sibilant is a noun but sibilate is not a noun.

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

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

sibilant (adjective)	sibilate (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)	sibilate (verb)
	make a sharp hissing sound, as if to show disapproval
	express or utter with a hiss
	utter a sibilant
	pronounce with an initial sibilant