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thief in the night, like a

According to the epistle to the Thessalonians in the New Testament, the “day of the Lord so cometh as a thief in the night.”

Note

By extension, “like a thief in the night” means to appear or arrive swiftly and stealthily: “This disease is like a thief in the night, stealing the thoughts and dreams of the elderly.”
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.