Wisp of smoke hiding silver feathers (7)
I believe the answer is:
plumage
'feathers' is the definition.
(I've seen this before)
'wisp of smoke hiding silver' is the wordplay.
'wisp of smoke' becomes 'plume' (I am not sure about this - if you are sure you should believe this answer much more).
'hiding' indicates putting letters inside.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'plume' going around 'ag' is 'PLUMAGE'.
Can you help me to learn more?
(Other definitions for plumage that I've seen before include "One's feathers" , "Birds' clothing" , "Cover for diver" , "coat" , "Bird's covering of feathers" .)