To take one is helpful (4)
I believe the answer is:
hand
'to take' is the definition.
The answer and definition can be both to do with ownership as well as being verbs in their base form.
Perhaps there's an association between them I don't understand?
'one is helpful' is the wordplay.
I cannot quite see how this works, but
'one' could be 'an' (I've seen this in other clues) and 'an' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hand that I've seen before include "Hired worker" , "Worker - four inches - bunch of bananas" , "audience response?" , "Unclenched fist" , "Help < and applause" .)