rosaryyoudaoicibaDictYouDict[rosary 词源字典]
rosary: [14] Rosary comes from Latin rosārium ‘rose garden’, a derivative of rosa ‘rose’. It was a common conceit in the Middle Ages to name collections of verse or similar short pieces after bunches of flowers (anthology comes from the Greek word for ‘flower’, and a similar inspiration underlies florilegium, while a 13thcentury volume of the collected works of the Persian poet Sa’di was called the Rose garden).

That was the background against which a collection of Roman Catholic prayers, consisting of Aves, Paternosters, and Glorias, came to be known as a rosary. A string of beads of varying sizes came to be used for counting off how far one has got in saying these prayers (English bead itself comes from a word meaning ‘prayer’), and this too was termed rosary.
=> rose[rosary etymology, rosary origin, 英语词源]
rosary (n.)youdaoicibaDictYouDict
"rose garden," mid-15c., from Latin rosarium "rose garden," in Medieval Latin also "garland; string of beads; series of prayers," from noun use of neuter of rosarius "of roses," from rosa "rose" (see rose (n.1)).

The sense of "series of prayers" is 1540s, from Middle French rosaire, a figurative use of the word meaning "rose garden," on the notion of a "garden" of prayers. This probably embodies the medieval conceit of comparing collections to bouquets (compare anthology and Medieval Latin hortulus animae "prayerbook," literally "little garden of the soul"). Sense transferred 1590s to the strings of beads used as a memory aid in reciting the rosary.