Is it correct to use the genitive case in: "The three Wise Men's Day"? Thank you!
Yes, because the possessive "'s" attaches to a phrase rather than to a word (or, at least, the last word of a phrase -- it's not clear). So, you could also have, for instance, "The people who wear tall hat's day is February 3." The structure is, for your example, [NP [Det [NP the three wise men ]'s ] day ], that is it's a noun phrase consisting of a determiner and a noun "day", where the determiner is a noun phrase with "'s" suffixed. Note the "the" does not go with "day", but rather with "men".
It's odd to have a suffix "'s" going with a phrase rather than with a word, so one is naturally suspicious of this structure which the sense of the construction seems to demand. Perhaps the "'s" actually attaches to the last word in the noun phrase, rather than to the noun phrase itself. You can test this by constructing examples with noun phrases ending in words which have irregular possessive forms, like me's ==> my. If it's really a word that the "'s" goes with, you should get the irregular possessive form. "February 12 is men who like me's day." versus "February 12 is men who like my day."
In English the Christian feast is commonly referred to as Epiphany and is celebrated January 6. In the Church of England, the eve of Epiphany is called the Twelfth Night and the first Monday after January 6 used to be known as Plough Monday.
I would advise the OP to avoid calling Epiphany as "Three Wise Men's Day". Although the Magi who visited the infant Jesus are also known as the Three Wise Men, the English feast is not named after them. The holiday which celebrates the birth of Jesus Christ is called Christmas and not Jesus's birthday, although that is an accurate description.
In countries across the world, Epiphany is called:
- In Argentina and Uruguay, the day is called "Día de Reyes" (The Day of Kings)
- In Bulgaria, Epiphany is celebrated on January 6 and is known as Bogoyavlenie ("Manifestation of God"), Кръщение Господне (Krashtenie Gospodne or "Baptism of the Lord") or Yordanovden ("Day of Jordan", referring to the river)
- The Dutch and Flemish call this day Driekoningen, while German speakers call it Dreikönigstag (Three Kings' Day).
- In Brazil, the day is called "Dia dos Reis" (The Day of Kings)
- In Finland, Epiphany is called loppiainen, a name which goes back to the 1600s. In the 1500s the Swedish-Finnish Lutheran church called Epiphany "Day of the Holy Three Kings", while before this, the older term Epiphania was used.
- In Greece, Cyprus and the Greek diaspora throughout the world, the feast is called the Theophany
- In parts of southern India, Epiphany is called the Three Kings Festival
- The Irish call it the Feast of the Epiphany or traditionally Little Christmas or "Women's Christmas"
- Epiphany is known in Latvia as Trijkungu diena (Three Kings Day)
- In Malta, Epiphany is commonly known as It-Tre Re (The Three Kings).
- In Poland, Epiphany is also called "Trzech Króli" (Three Kings)
- In Portugal, Epiphany, January 6, is called dia dos Reis (Day of the Kings)
- In Spain and some Latin American countries, Epiphany day is called El Día de los Reyes (The Day of the Kings)
Whilst gramatically this is correct, it's a bit fiddly and I would try to rephrase.
For example, rather than
The three wise men's day had been awful
You could try saying
The day had been awful for the three wise men
The day of the three wise man had been awful
Or you couls completely rephrase the question to be, as Janus pointed out:
The three wise men had had an awful day
As has also been pointed out, if you are refering to a holiday or pub for example, then that is correct (depending on what the holiday etc. is called,) however you would need to capitalise three as well:
"The Three Wise Men's Day" e.g. Our holiday at "The Three Wise Men's Day" was incredible