Fool, amusing or otherwise ... (9)
I believe the answer is:
ignoramus
'fool' is the definition.
(I've seen this before)
'amusing or otherwise' is the wordplay.
'otherwise' indicates an anagram.
'amusing'+'or'='amusingor'
'amusingor' with letters rearranged gives 'IGNORAMUS'.
(Other definitions for ignoramus that I've seen before include "Stupid person" , "Simpleton" , "Dunce" , "Idiot" , "Uninformed sort" .)