under cover

under cover idiom
  1. Protected by a shelter, as in It began to pour but fortunately we were under cover. [c. 1400]
  2. under cover of. Also, under the cover of. Hidden or protected by, as in They sneaked out under cover of darkness, or, as it was put in a sermon in 1751: “Presumption which loves to conceal itself under the cover of humility” (John Jortin, Sermons on Different Subjects).

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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