'Solemn' in the Bible

Bring no more vain oblations; incense is an abomination unto me; the new moons and sabbaths, the calling of assemblies, I cannot away with; it is iniquity, even the solemn meeting.

And in that day you will say,“Give thanks to the Lord, call on His name [in prayer].Make His deeds known among the peoples [of the earth];Proclaim [to them] that His name is exalted!”

The Lord who commands armies makes this solemn vow: "Be sure of this: Just as I have intended, so it will be; just as I have planned, it will happen.

“What shall I say?For He has spoken to me, and He Himself has done it;I will wander aimlessly all my years because of the bitterness of my soul.

“So I will profane the officials of the sanctuary,And I will consign Jacob to destruction and [I will subject] Israel to defamation and abuse.