Nunc, Sancte, nobis Spiritus is a Christian hymn which has traditionally been attributed to the fourth century St. Ambrose of Milan.
However the earliest manuscript tradition for the hymn seems to only go back to the ninth century.
[1] The hymn has traditionally been a core part of the prayers at Terce in the Liturgy of the Hours.
[2] As the Acts of the Apostles was so explicit in linking the Pentecost experience of the Apostles to the third hour of the day, Christian hymns and prayers intended to be used at that time of the day, have traditionally made reference to the coming of the Holy Spirit.
[3] The Plain Chant melodies used with the Latin version of the hymn changes according to the seasons in the Liturgical Year.