the word or definition is literally anti fascist shortened...
The English word antifa is a loanword from the German Antifa, taken as a shortened form of the word antifaschistisch ("anti-fascist") and a nickname of Antifaschistische Aktion (1932–1933), a short-lived group which inspired the wider Antifa movement in Germany.
Military practice by the local Communist Antifascist Society was broken up last night by police near the suburb of Heidemuehle. All members of the society, which is known as Antifa, were arrested and police are investigating purposes of the military practice, which they had suspected for a long time was taking place.
— The Daily Boston Globe, 20 Oct. 1930
'Antifa': the Word's Meaning, History, and Pronunciation | Merriam-Webster