Otherwise taken in by absurdly amusing fool (9)
I believe the answer is:
ignoramus
'fool' is the definition.
(thesaurus)
'otherwise taken in by absurdly amusing' is the wordplay.
'otherwise' becomes 'or'.
'taken in by' indicates putting letters inside.
'absurdly' is an anagram indicator (I've seen this in other clues).
'amusing' with letters rearranged gives 'ignamus'.
'or' going into 'ignamus' is 'IGNORAMUS'.
(Other definitions for ignoramus that I've seen before include "One is not intelligent" , "Fool" , "Stupid person" , "Ignorant person" , "At the present time" .)