Commonest word/letter for 'you' (4)
I believe the answer is:
thee
'for you' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for thee that I've seen before include "Old objective second person singular" , "'U'" , "You in the olden days" , "Poetically you" , "Quaker 'you'" .)