Surreptitious, furtive (8)
I believe the answer is:
stealthy
I believe this is a double definition.
'surreptitious' is the first definition.
(I know that surreptitious can be written as stealthy)
'furtive' is the second definition.
(I know that furtive can be written as stealthy)
(Other definitions for stealthy that I've seen before include "'Furtive, surreptitious (8)'" , "That's Ely (anag.)" , "Underhand" , "Moving surreptitiously" , "Secretive, silent" .)