it's a late medieval Latin, written by William Byrd, early 17th c.




Ave Verum Corpus natum
de Maria Virgine.
Vere passum immolatum
in cruce pro homine:
cuius latum perforatum
aqua fluxit et sanguine.
Esto nobis praegustatum
in mortis examine.

O Iesu dulcis!
O Iesu pie!
O Iesu Fili Mariae. Amen.
(or: O clemens, O pie
O dulcis Jesu, Fili Mariae.)

Hail, true Body, truly born
of the Virgin Mary mild.
Truly offered, wracked and torn,
on the Cross for all defiled,
from Whose love-pierced, sacred side
flowed Thy true Blood's saving tide:
be a foretaste sweet to me
in my death's great agony.

O my loving, Gentle One,
Sweetest Jesus,
Mary's Son. Amen.
(or: o gentle, o pious
o sweet Jeus, Son of Mary.)

(Translation by Fr. Edward Francis Garesche, SJ)