Comparatively slight bit of bother outside the pub (7)
I believe the answer is:
thinner
'comparatively slight' is the definition.
('thin' can be similar in meaning to 'slight')
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for thinner that I've seen before include "Diluting agent" , "Slenderer" , "Dissoving agent" , "what one adds to paint" , "Volatile liquid" .)