The four extinct days are called 四絕日 and mandarin and pronounced as si jue ri.
While the word 絕 can also be translated as absolute or even cold-blooded, the general consensus is that it means extinct in this respect.
The 4 extinct days refer to the 4 days during the year that is just before the commencement of the new seasons.
They are inauspicious as Qi would be at it’s weakest point of the season as it makes way for the next season to start.
Thus, they should be avoid as dates for activities where you don’t want to see a premature end to such as marriage and the commencement of business operations.
The four extinct days are:
- Coming of spring (立春)
- Coming of summer solstice (立夏)
- Coming of autumn equinox (立秋)
- Coming of winter solstice (立冬)
As the seasons are predictable the date of the 4 days can be determined as:
- February 3
- May 5
- August 8
- November 7
So cross out these dates from any important events or activities.