Reasonable, logical (8)
I believe the answer is:
rational
This clue is a double definition.
'reasonable' is the first definition.
(associated in meaning)
'logical' is the second definition.
(similar in meaning)
(Other definitions for rational that I've seen before include "Clearly thinking" , "Endowed with reason" , "Of sound mind -- not a liar (anag)" , "Able to reason" , "Reasoning, logical" .)