About a quarter will get better - truly (6)
I believe the answer is:
really
'truly' is the definition.
(I know that truly can be written as really)
'about a quarter will get better' is the wordplay.
'about' is an insertion indicator.
'a quarter will' becomes 'e' (I can't justify this - if you can you should believe this answer much more).
'get better' becomes 'rally' (I've seen this before).
'e' placed inside 'rally' is 'REALLY'.
Can you help me to learn more?
(Other definitions for really that I've seen before include "Well I never!" , "Indeed" , "without a doubt" , "In genuine way" , "Go on" .)