'assibilate' originates from Latin, specifically the verb 'sibilare', where 'sibilare' meant 'to hiss' and the prefix 'ad-' (meaning 'to, toward') was assimilated to 'as-' before 's' to form an element like 'assibil-'.

'assibilate' changed from Late Latin/Italian 'assibilare' (from Latin 'ad-' + 'sibilare') and was adopted into English (particularly in 19th-century and later linguistic literature) as 'assibilate'.

Initially it carried the sense 'to hiss or cause to hiss' (from 'sibilare'), and over time it has come to be used specifically in phonetics/phonology to mean 'to make or become sibilant' or 'to change a sound into a sibilant'.