The fears unravelling in Down (8)
I believe the answer is:
feathers
'down' is the definition.
(thesaurus)
'the fears unravelling' is the wordplay.
'unravelling' indicates an anagram.
'the'+'fears'='thefears'
'thefears' anagrammed gives 'FEATHERS'.
'in' acts as a link.
(Other definitions for feathers that I've seen before include "Plumage, insulation for birds" , "Plumages" , "Aids to flight" , "Bird insulation" , "''Hope is the thing with ...'' (Emily Dickinson)" .)