sincere UK /sɪnˈsɪə(ɹ)/US /sɪnˈsɪɹ/ adjective3 •really meaning what you say, and not hiding your true feelingsI believe he is sincere in his offer to help. •Meant truly or earnestly.She gave it a sincere if misguided effort. •(no longer used) Clean; pure. formsmore sincere · sincerer · most sincere · sincerest