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• eff
  eff

  verb (used with or without object)

  fuck.
• eff.
  eff.

  abbreviation

  efficient, efficiency.

eff

¹ American  

[ef] / ɛf /

verb (used with or without object)

effs, present (3rd person singular) effed, past participle, past effing present participle

1. fuck.

   Stop effing around and get to work!

   Eff you, you lout!

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noun

1. the word “fuck”; the f-word.

   peppering his speech with superfluous and highly offensive effs.

verb phrase

1. eff off Go away!.

   Eff off and die, you piece of Martian scum!

eff. ² American  

abbreviation

1. efficient, efficiency.

2. effective, effectiveness.

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eff British  

/ ɛf /

verb

1. taboo euphemism for fuck

   eff off

2. slang to use obscene language

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Other Word Forms

Derived Forms

• effing
  noun

Conjugated Forms

Present

• have effed
  perfect
• has effed
  perfect 3rd person singular
• am effing
  progressive 1st person singular
• have been effing
  perfect progressive
• has been effing
  perfect progressive 3rd person singular
• effing
  participle
• is effing
  progressive 3rd person singular
• are effing
  progressive
• effs
  singular 3rd person

Past

• had effed
  perfect
• was effing
  progressive singular
• had been effing
  perfect progressive
• effed
  participle
• effed
  simple
• were effing
  progressive plural

Future

• will eff
  simple
• will have effed
  perfect
• will have been effing
  perfect progressive
• will be effing
  progressive

Etymology

Origin of eff

1940–45; euphemism for fuck, with eff as spelled form of the name of the initial letter

Example Sentences

EFF leader Julius Malema hailed Friday's ruling, saying: "We are happy our Constitution has won."

From Barron's • May 8, 2026

Malema's prosecution came when Afrikaner lobby group AfriForum, which has a contentious relationship with him and the EFF, opened a case against Malema after the video went viral.

From BBC • Apr. 16, 2026

The San Francisco-based privacy and civil rights advocacy organization, also known as EFF, mapped out more than 40 hidden license plate readers in Southern California, most of them along border roadways.

From Los Angeles Times • Feb. 28, 2026

Erica Portnoy, a senior staff technologist at EFF, argues that “social media is just today’s satanic panic.”

From Salon • Feb. 11, 2026

The EFF did, in fact, eventually discover exactly how this figure was reached, and by whom—but only in 1991, long after the Neidorf trial was over.

From The Hacker Crackdown, law and disorder on the electronic frontier by Sterling, Bruce