assibilation vs sibilation

assibilation and sibilation both are nouns.

Word	Noun	Adjective	Verb	Adverb
assibilation	Yes	No	No	No
sibilation	Yes	No	No	No

As nouns, assibilation and sibilation are synonyms defined as:

assibilation and sibilation: pronunciation with a sibilant (hissing or whistling) sound

assibilation (noun)	sibilation (noun)
pronunciation with a sibilant (hissing or whistling) sound	pronunciation with a sibilant (hissing or whistling) sound
the development of a consonant phoneme into a sibilant	a fricative sound (especially as an expression of disapproval)