Something that is purposely kept from the view or knowledge of others either in violation of the law or to conduct or conceal some illegal purpose A "clandestine marriage" would be one which does not comply with laws related to publicity
Conducted with secrecy; withdrawn from public notice, usually for an evil purpose; kept secret; hidden; private; underhand; as, a clandestine marriage
a politically motivated unauthorized broadcasting station operating in secrecy, c f pirate
conducted with or marked by hidden aims or methods; "clandestine intelligence operations"; "cloak-and-dagger activities behind enemy lines"; "hole-and-corner intrigue"; "secret missions"; "a secret agent"; "secret sales of arms"; "surreptitious mobilization of troops"; "an undercover investigation"; "underground resistance"
Something that is clandestine is hidden or kept secret, often because it is illegal. their clandestine meetings. = secret. done or kept secret (clandestinus, from clam )