Truly reform mutual support (6)
I believe the answer is:
really
'truly' is the definition.
(I know that truly can be written as really)
'reform mutual support' is the wordplay.
I cannot really understand how this works, but
'support' could be 'ally' (I've seen this before) and 'ally' is located in the answer.
The remaining letters 're' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for really that I've seen before include "Honestly, it's a fact" , "Go on" , "without a doubt" , "Genuinely" , "Dead" .)