acenaphthylene

from The Century Dictionary.

• noun A hydrocarbon, C₁₂H₈, formed when the vapor of acenaphthene is passed over red-hot lead oxid.

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

• noun organic chemistry A polycyclic aromatic hydrocarbon containing an unsaturated five-membered ring ortho- and peri-fused to the 1- and 9- positions of naphthalene.