Secretive (8)
'secretive' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stealthy that I've seen before include "'Sneaky, clandestine (8)'" , "Done in a quiet or secretive way" , "Acting in furtive or covert manner" , "Moving surreptitiously" , "Acting in quiet or secret way" .)