Fatuous characters in Twain anecdote (5)
I believe the answer is:
inane
'fatuous' is the definition.
('inane' can be a synonym of 'fatuous')
'characters in twain anecdote' is the wordplay.
'characters in' indicates a hidden word.
'INANE' can be found hidden inside 'twain anecdote'.
(Other definitions for inane that I've seen before include "Fatuous, asinine" , "Idiotic" , "Frivolous" , "Foolish, fatuous" , "Dull-witted" .)