See sub rosa in Webster's New World Roget's A-Z Thesaurus II
adverb
In a secret way:
clandestinely, covertly, huggermugger, secretly. Idioms: by stealth, on the sly, under cover. See show
adjective
sub-rosaExisting or operating in a way so as to ensure complete concealment and confidentiality:
clandestine, cloak-and-dagger, covert, huggermugger, secret, undercover. (Informal) hush-hush. Idiom: under wraps. See show
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