Origin: 1920–25; < L sub rosā lit., under the rose, from the ancient use of the rose at meetings as a symbol of the sworn confidence of the participants
sub ro·sa (rō'zə) adv. In secret; privately or confidentially: held the meeting sub rosa.
[Latin sub rosā, under the rose (from the practice of hanging a rose over a meeting as a symbol of confidentiality) : sub, under + rosā, ablative of rosa, rose.] sub-ro'sa (səb-rō'zə) adj.