'assonantal' originates from Latin, specifically the word 'assonare' (via Late Latin 'assonantia'), where the prefix 'ad-' meant 'to/toward' and 'sonare' meant 'to sound'.

'assonantal' changed from Late Latin 'assonantia' and Old French 'assonance' into Middle English 'assonant', and eventually became the modern English adjective 'assonantal'.

Initially it meant 'the condition or quality of sounding alike (vocalic similarity)', but over time it evolved into its current adjectival sense of 'relating to or producing assonance'.