A banality that can grow into something big? (5)
I believe the answer is:
acorn
'a banality that can grow into something big?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'a banality' is the wordplay.
'banality' becomes 'corn' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'corn'='ACORN'
Can you help me to learn more?
(Other definitions for acorn that I've seen before include "From which a tall tree may grow" , "fruit in a cup" , "From which a mighty oak may grow?" , "from which something bigger may develop" , "Tree seed" .)