(also brimstone butterfly) a European butterfly of the white family, the male of which is yellow and the female greenish-white (Gonepteryx rhamni, family Pieridae). (also brimstone moth) a small yellow European moth (Opisthograptis luteolata, family Geometridae).
late Old Englishbrynstān, probably from bryne 'burning' + stān 'stone'
brimstone in other Oxford dictionaries
Definition of brimstone in the US English dictionary