decafPronunciation: /ˈdiːkaf/ (also decaff) informalTranslate decaf | into German Definition of decaf adjective decaffeinated:a decaff cappuccino a cup of decaf tea noun [mass noun] ( trademark in the UK) decaffeinated coffee: we haven’t any decaf, I’m afraidOrigin: 1950s: abbreviationdecaf in other Oxford dictionaries Definition of decaf in the US English dictionary