expression, godan verb (-tsu)
a tea stalk floats upright in one's cup (considered a sign of good luck)
A traditional Japanese superstition: if a tea stalk stands vertically in your cup, it is believed to bring good fortune. Often mentioned in casual conversation.
今朝、茶柱が立ったから、今日はいいことがありそうだ。
A tea stalk stood upright in my cup this morning, so I feel like something good will happen today.
The expression literally means 'a tea pillar stands'. It derives from the folk belief that an upright floating tea stalk is an omen of good luck.