The gas pipe cracked on Thursday.
I think I'm gonna do the laundry on Thursday.
On Thursday, do you want to do something fun like making a snowman or building an igloo?
This is a day of the week. You know this because it has 曜日 in it. But what day of the week is it? The tree day of the week is Thursday. Tree day comes after water day (which is Wednesday, for Water-Wednesday!). Trees need water to grow, which is why the tree comes right after the water.
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. It will help to know the word 曜日 as well.