1
general::
Phrase(s): in tune
in a state where musical notes are at their proper intervals so that none are flat or sharp. • Your piano is in tune. • The choir members all sang in tune.
McGrawhill's American Idioms And Phrasal Verbs
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general::
Also, in tune with. 1. In agreement in musical pitch or intonation, as in It's hard to keep a violin in tune during damp weather, or Dave is always in tune with the other instrumentalists. [Mid-1400s] 2. In concord or agreement, as in He was in tune with the times. [Late 1500s] The antonyms for both usages, dating from the same periods, are not in tune and out of tune, as in That trumpet's not in tune with the organ, or The lawyer was out of tune with his partners.
American Heritage Idioms