Century

As in, "It's was over 100 degrees F yesterday and it will breech the century mark today and tomorrow as well."

Century (n) - One hundred of something, be it years, degrees, soldiers. From the Latin, of course, centum, meaning 100. The rank of Centurion commanded a centuria of men in a Roman legion. Both words come from centum. That a centuria was only 80 men, not 100, is just proof of how hard it is to count using Roman numerals.