Fourday

As a standard Union Week has Ten Days instead of the traditional seven Terran Earth Humans use. Also the naming of the Weekdays has changed (At least officially, Most of the Union still uses OTT). The official begin of the Union Week starts with Oneday (same as Monday) Oneday is the begin of the Week, while Zeroday (Sunday) is the last Day.

Fourday is the fourth day in the Union Week (same as Thursday).

Other than that Fourday is just another weekday.