CONCERT, noun

1. Agreement of two or more in a design or plan; union formed by mutual communication of opinions and views; accordance in a scheme; harmony.

The allies were frustrated for want of concert in their operations.

The Emperor and the Pope acted in concert

2. A number or company of musicians, playing or singing the same piece of music at the same time; or the music of a company of players or singers, or of both united.

3. A singing in company.

4. Accordance; harmony.