One who doesn't eat more quickly? (6)
I believe the answer is:
faster
'more quickly?' is the definition.
('faster' can be a synonym of 'more quickly')
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for faster that I've seen before include "Person going hungry" , "One refuses to eat" , "Moving more quickly" , "More speedy" , "Speedier" .)