Some gentle doyen promoted song (5)
I believe the answer is:
yodel
'song' is the definition.
(thesaurus)
'some gentle doyen promoted' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'promoted' shows that the letters should be reversed in order (going up, in a down clue).
'ledoy' is hidden in the letters of 'gentle doyen'.
'ledoy' reversed gives 'YODEL'.
(Other definitions for yodel that I've seen before include "Sing by alternating between normal voice and falsetto" , "Alpine song or call" , "Falsetto singing" , "Sing (in the Alps)" , "unusual singing" .)