Sane (8)
'sane' is the definition.
(associated in meaning)
This is all the clue.
(Other definitions for rational that I've seen before include "Sane, based on logic" , "Logical; sensible" , "Endowed with reason" , "Sane and logical" , "Of sound mind -- not a liar (anag)" .)
'sane' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for logical that I've seen before include "clear" , "Based on reason" , "Deducible" , "Following correct reasoning" , "Correctly thought out" .)