The opposite of Tomorrow Night. The encapsulation of "tomorrow morning" and "tomorrow afternoon". Used to be more specific than just the word "tomorrow" which implies any given time between 12:00am and 11:59pm on the day after today but less specific than just "tomorrow afternoon" or "tomorrow morning".
Tomorrowday generally refers to the hours between 8am until the general hour that the sun starts to set (otherwise known as "tomorrow evening")
I'm staying up all night without any sleep. Why? This assignment is due sometime tomorrowday.