Undercover
Part of speech: adjective
Definition: Performed or happening in secret. Employed or engaged in spying or secret investigation.
Part of speech: noun
Definition: A person who works undercover.
Example sentence: I stay very much undercover and behind the scenes - most places I go, people don't know how important I am. But I will admit that my favorite piece of clothing to wear out is an old T-shirt from a Boston tour that does have a Boston logo. But that doesn't change anything.
Cloak-and-dagger
Part of speech: adjective
Definition: Marked by furtive secrecy, often with a melodramatic tint or espionage involved.