Definition of in tune
1 : in a state in which the correct musical sound is played or sung adjusted the guitar until it was in tune
2 : in a state in which people agree with or understand one another The president and his followers were clearly in tune. —usually + with The new supervisor is not in tune with the needs of the staff.
3 : in a state in which one thing agrees with or matches another —usually + with His formal clothing was in tune with the occasion.