Amazed by nonsense, laughed loudly (8)
I believe the answer is:
guffawed
'laughed loudly' is the definition.
('guffaw' can be a synonym of 'laugh loudly')
'amazed by nonsense' is the wordplay.
'amazed' becomes 'awed' (I've seen this before).
'by' says to put letters next to each other.
'nonsense' becomes 'guff' (I've seen this before**).
'awed' put after 'guff' is 'GUFFAWED'.
(Other definitions for guffawed that I've seen before include "Gave coarse noisy laugh" , "Laughed loudly" , "Roared" , "Was amused" .)