Spy aircraft's attribute (7)
I believe the answer is:
stealth
'spy aircraft's attribute' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stealth that I've seen before include "underhand dealing" , "Halt set in furtive manner" , "Secretiveness, furtiveness" , "By which taxes go up" , "word to define secrecy" .)