oxazole

from The Century Dictionary.

• noun The unknown mother- substance, C₃H₄ON, of compounds containing a ring composed of three carbon atoms, one nitrogen, and one oxygen atom.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry A five-membered heterocycle having three carbon atoms, one oxygen atom, one nitrogen atom and two double bonds; the 1,3- isomer is aromatic