PyrrolPyr"rol\, n. [Gr. ? flame-colored (from ? fire) + L. oleum oil.] (Chem.) A nitrogenous base found in coal tar, bone oil, and other distillates of organic substances, and also produced synthetically as a colorless liquid, C4H5N, having on odor like that of chloroform. It is the nucleus and origin of a large number of derivatives. So called because it colors a splinter of wood moistened with hydrochloric acid a deep red.