Tumbling, I fail, after missing right branch (9)
I believe the answer is:
affiliate
'branch' is the definition.
(thesaurus)
'tumbling i fail after missing right' is the wordplay.
'tumbling' is an anagram indicator.
'missing' suggests deleting specific letters.
'right' becomes 'r' (common abbreviation).
'fail'+'after'='failafter'
'failafter' with 'r' taken out is 'failafte'.
'i'+'failafte'='ifailafte'
'ifailafte' is an anagram of 'AFFILIATE'.
(Other definitions for affiliate that I've seen before include "Become closely connected" , "Associate with a parent body" , "Attach (to an organisation)" .)