Long cloud of smoke (5)
I believe the answer is:
plume
'long cloud of smoke' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for plume that I've seen before include "Feather; wisp of e.g. smoke" , "A fancy feather" , "Smoke when rising" , "Bunch of feathers" , "Large showy feather" .)