'Solemn' in the Bible

I will also cause all her mirth to cease, her feast days, her new moons, and her sabbaths, and all her solemn feasts.

What will ye do in the solemn day, and in the day of the feast of the LORD?

And I that am the LORD thy God from the land of Egypt will yet make thee to dwell in tabernacles, as in the days of the solemn feast.