Piece that is for one who's just started (6)
I believe the answer is:
rookie
'piece that is for one who's just started' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'piece that is' is the wordplay.
'piece' becomes 'rook' (rook is a kind of piece).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'rook'+'ie'='ROOKIE'
Can you help me to learn more?
(Other definitions for rookie that I've seen before include "Callow recruit" , "Slang for a new recruit" , "new team member" , "Beginner as in the army" , "Army or police recruit" .)