clandestine
/klan-ˈde-stən/
adjective
marked by, held in, or conducted with secrecy : surreptitious
a clandestine love affair
secret covert stealthy furtive clandestine surreptitious underhanded mean done without attracting observation. secret implies concealment on any grounds for any motive. covert stresses the fact of not being open or declared.