Chief trader exchanging diamonds for pounds (6)
I believe the answer is:
leader
'chief' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for leader that I've seen before include "Editorial - chief" , "Ruler" , "Opinion piece; boss" , "Head (of government, etc)" , "Front-runner or head of group" .)