Unprofessional friend into gold rejects lead (7)
I believe the answer is:
amateur
'unprofessional' is the definition.
(synonyms)
'friend into gold rejects lead' is the wordplay.
'friend' becomes 'mate' (mate is a kind of friend).
'into' is an insertion indicator.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'lead' says to take the initial letters.
The initial letter of 'rejects' is 'r'.
'mate' going into 'au' is 'amateu'.
'amateu'+'r'='AMATEUR'
(Other definitions for amateur that I've seen before include "Layperson" , "Unpaid or unskilled" , "Receiving no money" , "Lover" , "Dabbler" .)