undercover Synonyms

clandestine hugger-mugger hole-and-corner cloak-and-dagger underground secret hush-hush surreptitious secrecy back channel stealthily unseen underneath underhanded underhand stealthy subterranean subterraneous undergrow behind-the-scenes sub-rosa under cover top secret sneakily on the sly on the qt in disguise under-the-table surreptitiously confidentiality clandestinely in the dark unmarked camouflaged under wraps stealth spial furtively furtive disguised covertly covert covered confidential concealed closet cloaked classified blanketing backstairs