A painful growth but something beautiful will come of it (5)
I believe the answer is:
acorn
'something beautiful will come of it' is the definition.
I can't tell whether this definition defines the answer.
'a painful growth' is the wordplay.
'painful growth' becomes 'corn' (I have seen 'digital growth' mean 'corn' so perhaps 'growth' could also mean 'corn'. I am not sure about the 'painful' bit.).
'a'+'corn'='ACORN'
'but' is the link.
Can you help me to learn more?
(Other definitions for acorn that I've seen before include "Dirt on a liquid surface" , "Source of a great oak" , "Might source" , "From which a mighty oak may grow?" , "Oak seed" .)