Preposterous (6)
'preposterous' is the definition.
(synonyms)
This is all the clue.
(Other definitions for absurd that I've seen before include "irrational" , "'Ridiculous, silly (6)'" , "Preposterous, nonsensical" , "Ridiculous, ludicrous" , "word to describe Beckett's theatre!" .)
'preposterous' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for insane that I've seen before include "reckless" , "Quite mad" , "Mentally unhinged" , "Eg, gun or knife" , "Wild < cuckoo < cracked" .)
'preposterous' is the definition.
(rich can mean outrageous or unbelievable)
This is all the clue.
(Other definitions for rich that I've seen before include "Abundant" , "Well-off" , "elaborately decorated" , "Wealthy - luxurious - fruitful" , "having much wealth" .)
'preposterous' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for unbelievable that I've seen before include "Far-fetched" , "Incredible" , "Impossible to credit" .)
'preposterous' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for foolish that I've seen before include "Absurd, not sensible" , "Silly, unwise" , "Idiotic" , "Not very bright" , "Imprudent" .)