Old-fashioned pronoun (4)
I believe the answer is:
'old-fashioned pronoun' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for thee that I've seen before include "Poetically you" , "Archaic form of 'you'" , "Quaker 'you'" , "you many years ago" , "'U'" .)