A Latin (Vulgate) phrase whose literal meaning is "sing to the Lord". In liturgical settings, the "Cantate Domino" is a song (or chant) whose text is taken from Psalm 98. The "Cantate Domino" has existed in musical form as far back as the Gregorian chant (and probably earlier).
In the Anglican liturgy, the English translation of first two lines of the "Cantate Domino" follows:
O sing unto the Lord a new song for he hath done marvellous things.
With his own right hand, and with his holy arm hath he gotten himself the victory.