One trying to lose weight more quickly (6)
I believe the answer is:
faster
'more quickly' is the definition.
(synonyms)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for faster that I've seen before include "More speedy" , "One refuses to eat" , "Strafe (anag)" , "Quicker" , "Lent Observer" .)