noun
Metal Monkey month
Historical term from the traditional calendar. Refers to a lunar month that contains a day of the Metal Monkey (庚申), which occurs roughly every other month. It was believed that colds were more frequent during such months.
See also: 庚申
昔の暦では、庚申月は風邪をひきやすい月とされていた。
In the old calendar, the Metal Monkey month was considered a month when one was prone to catch colds.