Any of a large class of compounds characterized by a five-membered ring which contains an atom of nitrogen and at least one other noncarbon atom (nitrogen, oxygen, sulphur). The prefixes furo-, thio, and pyrro- are used to distinguish three subclasses of azoles, which may be regarded as derived respectively from furfuran, thiophene, and pyrrol by replacement of the CH group by nitrogen; as, furo-monazole. Names exactly analogous to those for the azines are also used; as, oxazole, diazole, etc.  [Webster 1913 Suppl.]