Some growth in knowledge is deliberate (5)
I believe the answer is:
think
'is deliberate' is the definition.
(I've seen this in another clue)
'some growth in knowledge' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'THINK' is hidden within 'growth in knowledge'.
(Other definitions for think that I've seen before include "figure" , "Meditate" , "Judge, consider" , "Cogitate; deem" , "Ponder" .)