sub rosa UK /ˌsʌb ˈɹəʊzə/US /ˌsʌb ˈɹoʊzə/adjective 2adverb 1noun 1forms 2 adjective2 •Carried out confidentially or secretly.He began a sub rosa campaign of obstruction, terror and depredation along the Thurn and Taxis mail routes. — 1966 •Not formally stated; implicit, tacit, unspoken. adverb1 •Covertly or in secret; confidentially, privately, secretly.They held the meeting sub rosa. noun1 •(US, slang) Covert surveillance video used as evidence against applicants for workers' compensation to show they are not in fact (seriously) injured. formsmore sub rosa · most sub rosa