azulene

noun

azu·lene

ˈazhəˌlēn

plural -s

: a liquid hydrocarbon C₁₅H₁₈ of intense blue color found in some essential oils (such as oil of cubebs) and in lignite tar

: any of various blue to violet or green hydrocarbons closely related chemically to this hydrocarbon and occurring naturally in essential oils or formed from various colorless naturally occurring sesquiterpenes

: a synthetic blue crystalline unsaturated bicyclic hydrocarbon C₁₀H₈ that resembles the isometric naphthalene in some properties but is more active chemically and that is the parent compound of the azulenes; cyclo-penta-cyclo-heptene