oratio

Oratio, orationis is feminine, third declension, from oro. The classical sense is a formal public speech, the thing Cicero delivered and then published, and by extension language or style: oratio soluta is prose, oratio recta and oratio obliqua are direct and indirect speech.

Church Latin takes the other half of oro, "I plead, I beg", and oratio becomes prayer. In a liturgical book an oratio is specifically a collect, the short prayer the priest says on behalf of everyone. In this corpus that is the dominant sense, so translating every oratio as "speech" will quietly turn a missal into a debating society. English oration, oratory and orator keep the classical branch; oratorio keeps the other.