tetraethyl leadPronunciation: /ˌtɛtrəˈiːθʌɪl/Definition of tetraethyl lead noun [mass noun] Chemistry a toxic colourless oily liquid made synthetically and used as an anti-knock agent in leaded petrol. Chemical formula: Pb(C2H5)4 tetraethyl lead in other Oxford dictionaries Definition of tetraethyl lead in the US English dictionary