* Lack of alliteration: This is the most straightforward option, simply stating that the text does not use alliteration.
* Assonance: While not a direct opposite, assonance focuses on the repetition of vowel sounds rather than consonant sounds.
* Consonance: Like assonance, consonance is a form of sound repetition, but it focuses on consonant sounds, which could be seen as a more distant, but still related, contrast to alliteration.
* No repetition of initial sounds: This focuses on the lack of the defining characteristic of alliteration.
Ultimately, the best "antonym" depends on the specific context and what you are trying to convey.