Strange sound up elm -- 1000 leaves drooping (9)
I believe the answer is:
pendulous
'drooping' is the definition.
(I know that drooping can be written as pendulous)
'strange sound up elm 1000 leaves' is the wordplay.
'strange' is an anagram indicator.
'1000' becomes 'M' (synonyms).
'leaves' suggests deleting specific letters.
'sound'+'up'+'elm'='soundupelm'
'soundupelm' with 'm' taken away is 'soundupel'.
'soundupel' is an anagram of 'PENDULOUS'.
(Other definitions for pendulous that I've seen before include "Dangling" , "Suspended" , "hanging heavy" , "Drooping" , "Hanging loosely" .)