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def

1 American  
[def] / dɛf /

adverb

Informal.

  1. definitely.

    Going to Europe this summer? But def!
def 2 American  
[def] / dɛf /

adjective

  1. Slang. excellent.

    That hip-hop record is def!
def. 3 American  

abbreviation

  1. defective.

  2. defendant.

  3. defense.

  4. deferred.

  5. defined.

  6. definite.

  7. definition.

def. 1 British  

abbreviation

  1. definition

"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
def 2 British  
/ dɛf /

adjective

  1. slang very good, esp of hip-hop

"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 def1

By shortening

Origin of def2

An Americanism dating back to 1980–85; of uncertain origin

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.

"If you're looking for a mental break from the world def get Pokopia, it's like therapy," US-based influencer Ashley Duncan wrote on X.

From Barron's • Mar. 11, 2026

James: 16 points, 4 steals, 5 rebounds in 17 minutes 👀🫡 Sierra Canyon def.

From Los Angeles Times • Jan. 19, 2025

There’s an intimacy to a book that we can’t get from a movie or a TV show, no matter how true it is — even in 3-D, in the highest of high def.

From New York Times • Apr. 27, 2023

“And we def have to catch up for drinks before you leave.”

From Washington Post • Apr. 7, 2023

“Oh, yes! I want to def —” He ignored her outburst.

From "Gathering Blue" by Lois Lowry

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.