quinolinePronunciation: /ˈkwɪnəliːn/Definition of quinoline noun [mass noun] Chemistry a pungent oily liquid present in coal tar. A heteroaromatic compound with fused benzene and pyridine rings; chemical formula: C9H7N Origin: mid 19th century: from Spanish quina (see quinine) + -ol + -ine4quinoline in other Oxford dictionaries Definition of quinoline in the US English dictionary