Thinner banker? (6)
I believe the answer is:
leaner
'thinner' is the definition.
('lean' is associated in meaning with 'thin')
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for leaner that I've seen before include "Thinner, with less fat" , "less productive" , "One with an inclination" , "less corpulent?" , "less bulky" .)