Uncertain, but probably an aphetic form of French alphonse (“kept man”), from the male given name Alphonse. Also sometimes connected to pounce or French pensionnaire (“pensioner, person living without working”).
ponce (plural ponces)
- (Britain, derogatory slang) A man living off another's earnings, especially a woman's.
- (Britain, Australia, Ireland, derogatory slang) Synonym of : an effeminate male homosexual; any similarly effeminate man. 
- 2000, Ben Kingsley as Don Logan, Sexy Beast:
- Thanks Don, see you Don, off to sunny Spain now Don, fuck off Don. Lying in your pool like a fat blob laughing at me, you think I'm gonna have that? You really think I'm gonna have that, ya ponce.
- (Britain, slang) To act as a pimp.
- (Britain, slang) Hence, to try to get rid of or proactively sell something.
- (Britain, derogatory) To behave in a posh or effeminate manner.
- 1992, Michael Swanwick, Stations of the Tide:
- The interior was warm and dim, cluttered with flying brass pigs and poncing felt mannequins.
- (Britain, slang) To borrow (something) from somebody without returning it.
ponce f (plural ponces)
- “ponce” in le Trésor de la langue française informatisé (The Digitized Treasury of the French Language).
ponce m (uncountable)
- punch (beverage)
- ponce in Treccani.it – Vocabolario Treccani on line, Istituto dell'Enciclopedia Italiana