assibilate
verb (used with object)
to change into or pronounce with the accompaniment of a sibilant sound or sounds.
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But in the classical period of the language, there is no reason for thinking that this assibilation existed, for the Greek transliterations of that period invariably denote Latin ti by τι, as Οὐαλεντία for Valentia.
From Latin Pronunciation A Short Exposition of the Roman Method by Harry Thurston Peck