We don't have synonyms for simulfix yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are similix and simuliid.
(n) :
(linguistics) A type of affix in which the change of meaning is conveyed by altering one or more existing phonemes in the affected morpheme, such as ablaut.
(n) :
(linguistics) A type of affix in which the change of meaning is conveyed by altering one or more existing phonemes in the affected morpheme, such as ablaut.