Part of the breviary containing the 'Day Hours' (horae diurnae), i.e. all the canonical hours except matins. After 1570, with the reformation of the service books by the Council of Trente, the Diurnale became the Officium Diurnum (see under this word). Cf. H. Bohatta, Bibliographie der Breviere, 1501-1850, 1937.