clandestine

secret, covert, stealthy, furtive, clandestine, surreptitious, underhanded mean done without attracting observation. secret implies concealment on any grounds for any motive <met at a secret location>. covert stresses the fact of not being open or declared <covert intelligence operations>. stealthy suggests taking pains to avoid being seen or heard especially in some misdoing <the stealthy step of a burglar>. furtive implies a sly or cautious stealthiness <lovers exchanging furtive glances>. clandestine implies secrecy usually for an evil, illicit, or unauthorized purpose and often emphasizes the fear of being discovered <a clandestine meeting of conspirators>. surreptitious applies to action or behavior done secretly often with skillful avoidance of detection and in violation of custom, law, or authority <the surreptitious stockpiling of weapons>. underhanded stresses fraud or deception <an underhanded trick>.