Look up sub rosa or under the rose in Wiktionary, the free dictionary.
The Latin phrase sub rosa (Neo-Latin for "under the rose"), denotes secrecy or confidentiality and is used in English to denote secrecy or confidentiality; this is somewhat in contrast to the Chatham House Rule which is an enforcement of non-attribution rather than secrecy. The rose has a long, ancient history as a symbol of secrecy.