(Fr.), apropos of boots—i.e. without real relevancy.
Chambers's Twentieth Century Dictionary (1908)
► uses
Uses:
"I've been bathing," said Mr. Chase, a propos des bottes.
"Oh," I replied. "And I wish," I added, "that you'd drowned yourself."
But I added it silently to myself.
P. G. Wodehouse. Love Among the Chickens A Story of the Haps and Mishaps on an English Chicken Farm (1909)
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Kitty Shtcherbatskaya, who had à propos de bottes poured out a stream of irrelevant absurdities with such spiteful fury, every nobleman with whom he had made acquaintance had become his adherent.