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Quondam is an adjective with a simple meaning: "former or something that once was." As in "the quondam president of the Basket Weaving Society," or, "the quondam Victorian mansion that sunk into the ground." Unlike other rare words, it doesn't take the place of a convoluted phrase or is more precise than a more common word; it's just fun to say!

Quondam is first attested to in the late 16th century, and comes from the Latin for "formerly."

Taken up and treated here.