Green’s Dictionary of Slang

keeping the passover phr.

[orig. known as hold a Rag Fair or hold a Monmouth Street. The association of Jewish old-clothes sellers with Monmouth Street led to the introduction of Passover, the Jewish spring festival commemorating the Exodus from Egypt; presumably + added ref. to the ‘passing over’ of the fresh air]

(W.I.) spreading out one’s clothes for an airing.

[UK] ‘Capt. Clutterbuck’s Champagne’ in Blackwood’s Mag. 655: Keeping the passover was, however, only a phrase at that time in vogue in Jamaica. It meant spreading out one’s kit or stock of clothes for the purpose of airing them. Its etymology was this: of yore the phrase had been, Holding a Rag Fair, or a Monmouth Street the displays being much like those of the children of Israel. One day, however, it flashed across the brain of an officer, who was a profound orientalist, that there was some historical connection between the passover and old clothes.