Te Deum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A hymn of praise to God sung as part of a liturgy.

Century Dictionary and Cyclopedia

1. An ancient hymn, in the form of psalm, sung at matins, or morning prayer, in the Roman Catholic and in the Anglican Church, and also separately as a service of thanksgiving on special occasions. The Te Deum is first mentioned early in the sixth century. Its authorship is popularly attributed to St. Ambrose and St. Augustine, but it probably assumed nearly its present form in the fourth century, during the Arian and Macedonian controversies, though in substance it seems to be still older, St. Cyprian in a. d. 252 using words closely similar to the seventh, eighth, and ninth verses, and several of the latter verses (“Day by day,” etc.) agreeing with part of an ancient Greek hymn, preserved in the Alexandrian Codex, the beginning of which is a form of the Gloria in Excelsis. Originally it was obviously modeled on the preface and great intercession of a primitive liturgy, probably African, of the type of the liturgy of St. James (see liturgy). In the Roman Catholic hour-offices the Te Deum is sung at the close of matins on Sundays and feast-days, but not in Advent nor from Septuagesima to Easter, except on feasts, and also in the ferial office from Easter to Pentecost. In the Anglican morning prayer, condensed from the Sarum matins, lauds, and prime, the Te Deum marks the close of matins. The Benedicite, taken from lauds, is used as its alternate, and in many churches the Te Deum is not sung in Advent or Lent. Also, more fully, Te Deum Laudamus.
2. A musical setting of this hymn.
3. Hence A thanksgiving service in which this hymn forms a principal part.

Wiktionary

1. n. An early Christian hymn of praise.
2. n. A religious service in which the singing of the hymn forms a principal part; a public thanksgiving.

GNU Webster's 1913

1. An ancient and celebrated Christian hymn, of uncertain authorship, but often ascribed to St. Ambrose; -- so called from the first words “Te Deum laudamus.” It forms part of the daily matins of the Roman Catholic breviary, and is sung on all occasions of thanksgiving. In its English form, commencing with words, “We praise thee, O God,” it forms a part of the regular morning service of the Church of England and the Protestant Episcopal Church in America.
2. A religious service in which the singing of the hymn forms a principal part.
3. A musical setting of the Te Deum{1}.

WordNet 3.0

1. n. an ancient liturgical hymn