2. A mark resembling a semicolon: chiefly attributive in semicolon butterfly, a North American butterfly, Polygonia interrogationis, which has a pale mark resembling a semicolon on the underside of its lower wings.
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1862 T. W. HarrisTreat. Insects Injurious to Vegetation (ed. 3) 289Vanessa interrogationis, Semicolon Butterfly... Under side of the wings in some rust-red..with a pale gold-colored semicolon on the middle of the hinder pair.