sibilation vs assibilation

sibilation and assibilation both are nouns.

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

As nouns, sibilation and assibilation are synonyms defined as:

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

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