eff

Short definition from Wiktionary

Noun

1. 1
   Alternative spelling of ef; the name of the Latin-script letter F/f.
2. 2
   Alternative letter-case form of eff.

Verb

1. 1
   Synonym of fuck.
2. 2
   To put into words; to express.

Proper noun

1. 1
   Initialism of Electronic Frontier Foundation.
2. 2
   Initialism of Economic Freedom Fighters.