Clandestine

"Clandestine" means:


 * 1) done, made, or acquired by stealth.
 * 2) acting or doing something clandestinely.
 * 3) marked by, held in, or conducted with secrecy :  surreptitious a clandestine love affair


 * Sources: https://www.merriam-webster.com/dictionary/surreptitious and https://www.merriam-webster.com/dictionary/clandestine