Hang on – it will be contingent upon (6)
I believe the answer is:
depend
'be contingent upon' is the definition.
(I've seen this before)
'hang on it' is the wordplay.
'hang' becomes 'pend' (I've seen this before).
'on' says to put letters next to each other.
'it' becomes 'de' (I can't justify this - if you can you should believe this answer much more).
'pend' after 'de' is 'DEPEND'.
'will' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for depend that I've seen before include "Be unable to do without, rely" , "Bank" , "Rest" , "Rely or hang on" , "Hang down or be connected to something" .)