What's the "een" in Halloween?
pyrrole pyr·role (pēr'ōl')
A five-membered heterocyclic ring compound that has an odor similar to chloroform and is the parent compound of hemoglobin, chlorophyll, and many other complex, biologically active substances. Also called imidole.
any of a class of organic compounds of the heterocyclic series characterized by a ring structure composed of four carbon atoms and one nitrogen atom. The simplest member of the pyrrole family is pyrrole itself, a compound with molecular formula C4H5N. The pyrrole ring system is present in the amino acids proline and hydroxyproline; and in coloured natural products, such as chlorophyll, heme (a part of hemoglobin), and the bile pigments. Pyrrole compounds also are found among the alkaloids, a large class of alkaline organic nitrogen compounds produced by plants.