This carol was/is used to celebrate the Feast of the Holy Innocents, December 28, and is named after the city of Coventry where the 15th Century Pageant of the Shearmen and Tailors of the Coventry Cycle was held. It tells of Herod's slaughter of the innocents upon which the lyrics are based. A piano score and copious notes are given in Elisabeth Poston's The Penguin Book of Christmas Carols and is very similar to the version sung by Tyneside Maritime Chorus who have it in their Christmas repertoire.
This song may be found in the Tyneside Maritime Chorus songbook

Lyrics