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Mr. Cool

American  

noun

Informal.

  1. a person who is ideally or excessively self-possessed, poised, or reserved (sometimes used with Miss, Ms., or Mrs. instead of Mr. when referring to a female).

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

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