'Solemn' in the Bible

Six days thou shalt eat unleavened bread: and on the seventh day shall be a solemn assembly to the LORD thy God: thou shalt do no work therein.

Seven days shalt thou keep a solemn feast unto the LORD thy God in the place which the LORD shall choose: because the LORD thy God shall bless thee in all thine increase, and in all the works of thine hands, therefore thou shalt surely rejoice.