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in key

In harmony with other factors, in a matching style, as in This furniture is perfectly in key with the overall design. This term uses key in the musical sense, that is, “a scheme of notes related to one another.” The antonym, out of key, means “not in harmony with other factors,” or “unsuitable,” as in He is out of key with his time. [c. 1900]

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The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.