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EO

1 American  

  1. executive order.

eo- 2 American  

  1. a combining form meaning “early,” “primeval,” used in the formation of compound words.

    Eocene; eohippus.
e.o. 3 American  

abbreviation

  1. ex officio.

e.o. 1 British  

abbreviation

  1. ex officio

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
eo- 2 British  

combining form

  1. early or primeval

    Eocene

    eohippus
"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of eo-

< Greek, combining form of ēṓs ( Attic héōs ) dawn; akin to east, Aurora

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

“We see the signing of this EO as a substantial step towards diminishing regulatory risk in this emerging class of therapies, enabling investor comfort,” RBC Capital Markets analyst Brian Abrahams told investors.

From MarketWatch • Apr. 20, 2026

EO: I was thinking about it the other day for the first time, believe it or not.

From Los Angeles Times • Sep. 10, 2025

For example, in the case of EO, highly corrosive hydrogen fluoride vapor.

From BBC • Aug. 18, 2025

“Straws are just the beginning,” Matt Seaholm, president and CEO of the Plastics Industry Association, said in a statement after Trump signed the EO.

From Slate • Feb. 12, 2025

"Even super-low EO? We might be able to—" "Loss of signal, Flight."

From "The Martian" by Andy Weir

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.