Here are some options depending on the context:
For musical polyphony:
* Counterpoint: This is the most direct synonym, referring specifically to the technique of combining multiple independent melodic lines.
* Multi-voiced: This emphasizes the multiple voices involved.
* Harmonic texture: This focuses on the resulting sound and the interplay of different harmonies.
* Heterophony: Specifically refers to when multiple voices play the same melody with slight variations.
For polyphony in literature and rhetoric:
* Multivocality: This emphasizes the presence of multiple voices or perspectives.
* Dialogue: This implies a conversation or exchange of ideas between different viewpoints.
* Intertextuality: This refers to the way texts reference and interact with other texts.
Ultimately, the best alternative word depends on the specific context and the nuance you want to convey.