Bit of a cloud (4)
I believe the answer is:
wisp
'bit of a cloud' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for wisp that I've seen before include "Small thin line of cloud or smoke" , "Gauzy strand" , "(Smoke) thin plume" , "Light streak of smoke or stray hair" , "whose will is so elusive?" .)