The American Church Dictionary and Cycopedia
The term "office," in ecclesiastical usage, means a formulary of devotions; a form of service appointed for a particular occasion; a prescribed form or act of worship; thus the Daily Morning and Evening Prayer are called the "Daily Offices." The word is commonly used of the various services set forth in the Prayer Book, as "Baptismal Office," "Communion Office," etc.
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Miller, William James. Entry for 'Office'. The American Church Dictionary and Cyclopedia. https://www.studylight.org/dictionaries/eng/acd/o/office.html. 1901.