sneaky

Adjective

• marked by quiet and caution and secrecy; taking pains to avoid being observed
  • a furtive manner
    
  • a sneak attack
    
  • stealthy footsteps
    
  • a surreptitious glance at his watch
    

• marked by deception
  • achieved success in business only by underhand methods
    

Related words

• Synonyms: 
  furtive , sneak(a) , stealthy , surreptitious , underhand , underhanded