monologue

English borrowed 'monologue' from Middle French monologue around 1550, which was itself modeled on 'dialogue' and traces back to Byzantine Greek μονόλογος (monólogos), from mono- 'single' and lógos 'speech, word.'

The word entered English already shaped by the French pattern of pairing it with 'dialogue,' so its sense of 'one person speaking alone' was fixed from the start.

It shares its second half with 'dialogue,' since French coined 'monologue' directly on that model, both ultimately resting on Greek lógos.