Plum to throw at the bottom of copper (5)
I believe the answer is:
cushy
'plum to' is the definition.
I can't tell whether this definition defines the answer.
'throw at the bottom of copper' is the wordplay.
'throw' becomes 'shy' (shy can mean to throw or sling).
'at the bottom of' says to put letters next to each other (in a down clue, some letters go below others).
'copper' becomes 'cu' (Cu is the chemical symbol for copper).
'shy' after 'cu' is 'CUSHY'.
Can you help me to learn more?
(Other definitions for cushy that I've seen before include "Not demanding" , "Simple" , "Comfortable" , "(Of situation) secure, easy (colloq.)" , "16 21 [INDIAN IMPORT]" .)