A mixture of nonvolatile hydrocarbons, derivatives of catechol with unsaturated C15 or C17 side chains, constituting the active allergen of the irritant oil of poison ivy, Toxicodendron radicans, poison oak, T. diversilobum, and the Asiatic laquer tree, T. verniciferum.
[Jap. urushi, lac, + L. oleum, oil]
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Examples: glitazone, GI cocktail, etc.