Illogical, absurd (10)
I believe the answer is:
irrational
I believe this is a double definition.
'illogical' is the first definition.
(associated in meaning)
'absurd' is the second definition.
(I've seen this in another clue)
(Other definitions for irrational that I've seen before include "Unreasonable" , "Illogical" , "making no sense" , "Not logical" , "nuts" .)