monophonous
Able to produce only one sound at a time.
Characterized by monophony.
It was a short monophonous melody with a delicate Oriental redolence, much like a lullaby or love song.
Where it comes from
From mono- + -phonous. Compare Ancient Greek μονόφωνος (monóphōnos, “with only one voice or tone”).
Adapted from the Wiktionary entry monophonous (CC BY-SA 4.0).