under the impression

under the impression idiom
Thinking, assuming, or believing something, as in I was under the impression that they were coming today. This idiom often suggests that the idea or belief one had is mistaken. [Mid-1800s]

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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