In many churches today is the Fourth Sunday after Easter, Cantate Sunday, so named because the first words of the Mass introit are Cantate Domino novum canticum, “Sing ye to the Lord a new song.”
Obsessed recently with writing deadlines, I missed a couple named traditional Sundays on the Christian calendar. The first Sunday after Easter (April 12 this year) is sometimes called Octave Day of Easter, and also St. Thomas Sunday, Divine Mercy Sunday, and Quasimodo Sunday (or Quasimodogeniti). The latter comes from the Latin Quasi modo geniti infantes, "like [or in the manner of] newborn infants," which is the text of the Introit from 1 Peter 2:2
The Third Sunday after Easter (April 26 this year) is Jubilate Sunday, named because the introit of the Catholic liturgy begins Jubilate Deo omnis terra ("Shout with joy to God, all the earth") from Psalm 65.