first thing

first thing idiom
Before anything else; without delay. For example, Tom was supposed to call him first thing in the morning. [Late 1500s] Also see under first and foremost; first off.

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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