1Of an instrument, the voice, etc.: finely or properly tuned; having a good tone; (of music or sound) tuneful, melodious. Also of a group of musicians, etc.: in good harmony.
2Of the ear, etc.: highly attuned to or appreciative of music, melody, or harmony.
3Characterized by or exhibiting euphony, balance, or apt arrangement.
4Of an engine, motor vehicle, etc.: having its moving parts carefully adjusted so as to run smoothly and efficiently; in good working order or condition.
Mid 16th century; earliest use found in Biblia: the Bible. From well + tuned.