Clandestine
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
Secret; hidden; concealed. The "clandestine importation" of goods is a term used in English statutes as equivalent to "smuggling."
Keck v. U. S., 172 U. S. 434, 19 Sup. Ct 254, 48 In Ed. 505.
A clandestine marriage is (legally) one contracted without observing the conditions precedent prescribed by law, such as publication of bans, procuring a license or the like.