styrenePronunciation: /ˈstʌɪriːn/Definition of styrene noun [mass noun] Chemistry an unsaturated liquid hydrocarbon obtained as a petroleum by-product. It is easily polymerized and is used to make plastics and resins. Chemical formula: C6H5CHCH2 Origin: late 19th century: from styrax + -enestyrene in other Oxford dictionaries Definition of styrene in the US English dictionary