Lucky Day
Noun
かじつ
本日は、皇太子殿下御生誕の嘉日なり。
It’s the auspicious day of the Crown Prince’s birth today.
A day you hold in high esteem is an auspicious day. That's a fancy way of saying it's a really lucky day!
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.