eff

verb

ˈef 

effed; effing; effs

transitive + intransitive

informal

—used as a euphemism for fuck in various senses of the word

You don't eff with [=mess with] the Tupac legacy. You just don't.

—Olivia Jade Khoury

A guy who likes you a bit more than you like him generally … doesn't eff with your mind.

—Jessica Knoll

She told them to eff off [=scram].

… he sees this age of mass travel, mass entertainment and mass culture as the best of all possible ages. Anyone who disagrees, he snarls, had better eff off now.

—Robert Carver

Did they do everything perfectly? No, they effed up [=messed up] a lot of stuff.

—Lawrence Yee

Toronto city council huffed and puffed, the Ford brothers blustered and bullied, the mayor even admitted to buying drugs while in office, and there were renewed apologies: "There is nothing else to say, guys. I really effed up [=messed up]."

—Toronto Star

They threatened to eff him up if he didn't cooperate.

He says something at the end of the movie that effed me up [=upset or shocked me].

—Teresa Jusino

Examples of eff in a Sentence

Recent Examples on the Web

Build a Sandbox Even though agents are actually good now, the rascally little devils can still eff everything up without proper boundaries. —Reece Rogers, Wired News, 26 May 2026

Netflix is looking to eff up your summer with a second season of FUBAR, dropping in its entirety on Thursday, June 12, TVLine has learned. —Andy Swift, TVLine, 3 Apr. 2025

In this very twisted take on the Bambi story, our deer — now not simply grief-stricken over the death of his mother but also mutated, effing enormous and sporting an array of sharp, terrifying teeth — embarks on a deadly rampage through the woods seeking revenge. —Alex Ritman, Variety, 5 Mar. 2025

After all, hair grows from the root, so don't eff it up by putting stress on your root. —Jihan Forbes, Allure, 25 Oct. 2021

Word History

Etymology

spelling variant of ef, representing the initial letter of fuck entry 1

First Known Use

1938, in the meaning defined above