solemnity

noun

1. (countable, uncountable)The quality of being deeply serious and sober or solemn.

   “the solemnity of a funeral”

   “The stateliness and gravity of the Spaniards shows itself in the solemnity of their language.”

   “These promises were often made with great solemnity and confirmed with an oath.”

   “There has been nothing in archæology that has made such a vivid impression on the popular imagination as Mr. Arthur Evans's excavations at Knossos. The Minotaur! the Labyrinth—such words do not suggest the solemnities of antiquarian research.”

2. (countable, uncountable)An instance or example of solemn behavior; a rite or ceremony performed with reverence.

   “Great was the cauſe; our old ſolemnities / From no blind zeal or fond tradition riſe, / But ſav'd from death, our Argives yearly pay / Theſe grateful honours to the God of Day.”

   “This is the Man after God's Heart, […] by endeavouring, when he aſſiſted at thoſe Solemnities, to perform them with the utmoſt Attention, Alacrity, and holy Warmth of Mind, of which he was capable.”

3. (countable, uncountable)A feast day of the highest rank celebrating a mystery of faith such as the Trinity, an event in the life of Jesus, the Virgin Mary, or another important saint.
4. (countable, uncountable)A solemn or formal observance; proceeding according to due form; the formality which is necessary to render a thing done valid.
5. (countable, obsolete, uncountable)A celebration or festivity.