You get the key (4)
I believe the answer is:
thee
'you' is the definition.
(historical second person pronoun)
'get the key' is the wordplay.
'get' means one lot of letters go next to another.
'key' becomes 'e' (musical key).
'the' next to 'e' is 'THEE'.
(Other definitions for thee that I've seen before include "Archaic form of 'you'" , "You (arch.)" , "Quaker 'you'" , "Poetically you" , "Old objective second person singular" .)