'Solemn' in the Bible

Also in the day of your gladness, and in your solemn days, and in the beginnings of your months, ye shall blow with the trumpets over your burnt offerings, and over the sacrifices of your peace offerings; that they may be to you for a memorial before your God: I am the LORD your God.

And will make an offering by fire unto the LORD, a burnt offering, or a sacrifice in performing a vow, or in a freewill offering, or in your solemn feasts, to make a sweet savour unto the LORD, of the herd, or of the flock:

On the eighth day ye shall have a solemn assembly: ye shall do no servile work therein: