Previously used in poetry (3)
I believe the answer is:
ere
'previously used in poetry' is the definition.
(I've seen this in another clue)
'previously used in poetry' is the wordplay.
'previously' becomes 'er' (I can't explain this - if you can you should believe this answer much more).
'used in' means to look at the middle letters (the letters used on the inside of the word).
'poetry' becomes 'poesy' (synonyms).
The middle letter of 'poesy' is 'e'.
'er'+'e'='ERE'
Can you help me to learn more?
(Other definitions for ere that I've seen before include "Archaic word for before - a palindrome" , "Old word for before" , "Before (in time)" , "Old prior" , "Before (lit.)" .)