What is "acenaphthylene"

n. (context organic compound English) A polycyclic aromatic hydrocarbon containing an unsaturated five-membered ring ortho- and peri-fused to the 1- and 9- positions of naphthalene.

Acenaphthylene is a polycyclic aromatic hydrocarbon. The molecule resembles naphthalene with positions 1 and 8 connected by a CH unit. It is a yellow solid. Unlike many polycyclic aromatic hydrocarbons, it has no fluorescence.