A breviary was an approved book by the church used for hymns which are typically songs of worship or praise. A breviary would also be used for prayers for the canonical hours recited daily by clerics in religious orders. Another way of saying this is a set of daily prayers which were to recited at a certain hour of the day as appointed by the priests of the time.

Sources:

Merriam Webster. “Breviary.” merriam-webster.com,https://www.merriam-webster.com/dictionary/breviary

Croce Benedetto and Hiroko Fudemoto. Breviary of Aesthetics: Four Lectures.University of Toronto Press, Scholarly Publishing Division, 2007. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=nlebk&AN=682605&site=eds-live&scope=site.