Te DeumPronunciation: /tiː ˈdiːəm, teɪ ˈdeɪəm/Definition of Te Deum noun a hymn beginning Te Deum laudamus, ‘We praise Thee, O God’, sung at matins or on special occasions such as a thanksgiving. an expression of thanksgiving or exultation. Origin:LatinTe Deum in other Oxford dictionaries Definition of Te Deum in the US English dictionary