In Latin, it means, "under the rose." The term originates in Roman mythology. One story says that the child god Harpocrates surprised Venus while she was engaged in an illicit romance. Her son, Cupid, offered Harpocrates a beautiful rose to keep quiet. The rose became a symbol of silence. In medieval times, hanging a rose from the ceiling during a meeting was a reminder that any statements made "under the rose" were to be kept in confidence. Painted roses and plaster roses in room decorations continued this tradition for centuries.

In secret; privately or confidentially: held the meeting sub rosa.