Noun and の adjective
しゅくじつ
コウイチは祝日はいつもかなり派手な格好をしている。
Koichi always wears the most showy clothes on holidays.
A celebrate day is a day you get off to celebrate something awesome. This is also known as a holiday. Festivus for the restivus!
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.