solemnity

noun5

1. •
   The quality of being deeply serious and sober or solemn.

   • The stateliness and gravity of the Spaniards shows itself in the solemnity of their language. — 1711
2. •
   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. — 1699
3. •
   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. •
   A solemn or formal observance; proceeding according to due form; the formality which is necessary to render a thing done valid.
5. •
   (no longer used) A celebration or festivity.