From Longman Dictionary of Contemporary Englishsub-zeroˌsub-ˈzero adjective [usually before noun]TMTHEMbelow zero in temperaturesub-zero weather/temperaturesExamples from the Corpussub-zero• The 37-year-old took an overdose of painkillers and lay in sub-zeroconditions with just a sleepingbag.• Until now the harddiscipline to follow through has rousted me outdoors on sub-zero days even before daylight.• Prisoners, unable to exerciseoutside in sub-zero temperatures, had been allowed longer in the recreationrooms.• During previews, in sub-zero temperatures, the audiences were thin and seemed a little confused.• Part of the M1 was closed for the second time in three days following a multiple pile-up in sub-zero temperatures.sub-zero weather/temperatures• Part of the M1 was closed for the second time in three days following a multiple pile-up in sub-zero temperatures.• Prisoners, unable to exercise outside in sub-zero temperatures, had been allowed longer in the recreation rooms.• During previews, in sub-zero temperatures, the audiences were thin and seemed a little confused.