solemnity

A solemnity is a feast day of the highest rank in the liturgical calendar of the Roman Rite, celebrating a mystery of faith such as the Trinity, an event in the life of Jesus, his mother Mary, or another important saint. The observance begins with the vigil on the evening before the actual date of the feast. Unlike feast days of the rank of feast (other than feasts of the Lord) or those of the rank of memorial, solemnities replace the celebration of Sundays outside of Advent, Lent and Easter (those in Ordinary Time).