Decaf™
noun /ˈdiːkæf/
  /ˈdiːkæf/
(also decaff)
 (both British English) (North American English decaf)
 [uncountable, countable] (informal)- decaffeinated coffee
- (British English) Regular coffee or Decaf?
 - I'll have a decaff, please.
 
Word Origin1960s: abbreviation.