Feathers end up exciting wonder (9)
I believe the answer is:
eiderdown
'feathers' is the definition.
(eiderdown is a kind of feathers)
'end up exciting wonder' is the wordplay.
'end' becomes 'die'.
'up' is a reversal indicator (in down clue: letters go upwards).
'exciting' indicates anagramming the letters.
'die' written backwards gives 'eid'.
'wonder' is an anagram of 'erdown'.
'eid'+'erdown'='EIDERDOWN'
(Other definitions for eiderdown that I've seen before include "Soft quilt filled with duck feathers" , "Warm bed cover" , "What might keep one warm" , "Warm bedcover" , "what keeps retired people warm" .)