The gang will hold their arranged meeting (9)
I believe the answer is:
gathering
'meeting' is the definition.
('gather' can be a synonym of 'meet')
'the gang will hold their arranged' is the wordplay.
'will hold' indicates putting letters inside (inserted letters are held inside).
'arranged' indicates an anagram (letters rearranged).
'their' with letters rearranged gives 'theri'.
'gang' enclosing 'theri' is 'GATHERING'.
(Other definitions for gathering that I've seen before include "Assembly, meeting" , "convention?" , "Assembly; a boil" , "Harvesting" , "party" .)