To adjust until resonant — an instrument to true pitch, a sound to its intended shape. The bringing of a thing into agreement with itself.
Middle English tune, a variant spelling of tone, from Latin tonus (a tone, stretching), from Greek tonos, named the adjusting of a sound until it agrees with its intended shape.
The adjusting of a sound or instrument until it agrees with itself, the bringing of a thing into resonance with its own intended shape.