Thin strand (4)
I believe the answer is:
wisp
'thin strand' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for wisp that I've seen before include "Slight trace" , "Small streak of smoke or cloud" , "Gauzy strand" , "whose will is so elusive?" , "Small thin bunch/strand (of something)" .)