However, depending on what you're trying to express, you could consider these options:
Focusing on sound contrast:
* Consonance: This focuses on the repetition of consonant sounds, offering a direct contrast to the vowel repetition in assonance.
* Dissonance: While it doesn't specifically target vowels, it implies a lack of harmonious sounds, which could be considered the opposite of the pleasing effect of assonance.
Focusing on the absence of repetition:
* Variation: This broadly refers to the use of diverse sounds and avoiding repetition.
* Heterophony: This specifically describes the use of different vowel sounds, which would directly oppose the repetition found in assonance.
Focusing on the intended effect:
* Dissonance: If assonance aims to create a pleasing or rhythmic effect, dissonance would aim to create a jarring or unpleasant effect.
* Harmony: This encompasses a broader sense of pleasing sounds, and would suggest a lack of assonance's distinct vowel repetition.
Ultimately, the "antonym" you choose will depend on the specific context and the effect you are aiming for.