From Longman Dictionary of Contemporary Englishdouble dutyˌdouble ˈduty noun → do double duty
Examples from the Corpus
double duty• The demonstrator will be doing double duty.• But many food plants are beautiful in their own right and fit for double duty in the pleasure garden.• Aseptic boxes of fruit juices or plastic containers of prepared beverages can be frozen to serve double duty in the cooler. 