Dentah Calendar

The Dentah calendar is based on a year of 371 days. Neatly divided into ten months of 35 days and one month of 21 days: Aímas. Each month is divided further into five weeks of seven days.
The year begins in summer. And each season has 2 months to their own. The last two months are shared. One between Spring and Summer and one between Autumn and Winter.
Pr=Primary or the first month that belongs solely to that season. Sec=Secondary or the second month that belongs solely to that season. Dy=Dyad or the transition month from spring to summer and autumn to winter.
Sum=Summer, Aut=Autumn, Win=Winter, Spr=Spring

Ménti	Aéras	Astrapí	Nerós	Skiás	Athér	Aímas	Zontan	Gï	Fos	Fearna
Summer Sec.	Autumn Pr.	Autumn Sec.	Aut./Win. Dy.	Winter Pr.	Winter Sec.	Decay	Spring Pr.	Spring Sec.	Spr./Sum. Dy.	Summer Pr.
Psychic	Air	Lightning	Water	Shadow	Ethereal	Anti-magic	Nature	Earth	Radiant	Fire

The Dentah calendar month is based on the cycle of the Moon(Lycas) and is exactly 35 days long. Due to this Lyca is full for 4 consecutive days every month.
The week or Haiph in the original Dentah calendar is based on Haiphas. The week begins when the first sliver of the Haiphas can be seen. And ends when it disappears.

The table shows the week days with the corresponding phase of Haiphas and the words the weekday is derived from.

Nephas	Fhalphas	Haiphax	Fulphas	Haiphan	Shalphas	Darphas
Waxing Crescent	First Quarter	Waxing Gibbous	Full Moon	Waning Gibbous	Third Quarter	Waning Crescent /New Moon
New Haiphas	First half Haiphas	Haiphas Waxing	Full Haiphas	Haiphas Waning	Second half Haiphas	Dark Haiphas

The calendar changes from year to year but is periodic with a period of 25 years. So the calendar in 425 is the same as the one in 450.

History of the Dentah Calendar

The Dentah calendar was from the empire that spanned the whole of Gainesh. (The language is based on Ancient Greek) They noted the year can be evenly divided into the cycle of Haiphas. And further devided into months linked to the elements. And one month were sacrifices were made to ensure spring would come again. This sacrificial week is called Aímas or blood in the original Dentah. Due to the tendency for some numbers to appear they considered these numbers holy: 3*7*17=357. 3 for the Lunar Ternion. 7 for the length of Haiphas cycle. 17 they called the hidden holy number.

The calendar

You can see the calendar at https://donjon.bin.sh/fantasy/calendar/
Add the following code in the save/restore section if that doesn't work add } twice to the end.

{"year_len":371,"events":1,"n_months":11,"months":["Ménti","Aéras","Astrapí","Nerós","Skiás","Athér","Aímas","Zontan","Gï","Fos","Fearna"],"month_len":{"Ménti":35,"Aéras":35,"Astrapí":35,"Nerós":35,"Skiás":35,"Athér":35,"Aímas":21,"Zontan":35,"Gï":35,"Fos":35,"Fearna":35},"week_len":7,"weekdays":["Nephas","Fhalphas","Haiphax","Fulphas","Haiphan","Shalphas","Darphas"],"n_moons":3,"moons":["Haiphas","Lycas","Calas"],"lunar_cyc":{"Haiphas":7,"Lycas":35,"Calas":175},"lunar_shf":{"Haiphas":6,"Lycas":6,"Calas":0},"year":3444,"first_day":0,"notes":{"3425-4-25":"Taria campaign date","3424-9-16":"Beginning Taria Campaign","3446-2-2":"Folly of the Phoenix Campaign"
Worldanvil also has a calendar editor but the moons are not yet accurate: