The Collaborative International Dictionary of English v.0.48:

Clandestine \Clan*des"tine\, a. [L. clandestinus, fr. clam
   secretly; akin to celare, E. conceal: cf. F. clandestin.]
   Conducted with secrecy; withdrawn from public notice, usually
   for an evil purpose; kept secret; hidden; private; underhand;
   as, a clandestine marriage. --Locke.

   Syn: Hidden; secret; private; concealed; underhand; sly;
        stealthy; surreptitious; furtive; fraudulent. --
        Clan*des"tine*ly, adv. -- Clan*des"tine*ness, n.
        [1913 Webster]