WordNet sense 1 (a covering that serves to conceal or shelter something):

concealment, cover, screen

WordNet sense 2 (kept safe or defended from danger or injury or loss):

protected, secure

WordNet sense 3 (lying beyond what is openly revealed or avowed (especially being kept in the background or deliberately concealed)):

ulterior

WordNet sense 4 (communicated covertly):

secret

WordNet sense 5 (having its true character concealed with the intent of misleading):

disguised

WordNet sense 6 (conducted with or marked by hidden aims or methods):

surreptitious

WordNet sense 7 (secret and sly or sordid):

furtive