'Solemn' in the Bible

I will also cause all her celebrations to cease: her feasts, her new moons, her Sabbaths, and all her solemn assemblies.

What will you do in the day of solemn assembly, and in the day of the feast of Yahweh?

"But I am Yahweh your God from the land of Egypt. I will yet again make you dwell in tents, as in the days of the solemn feast.