Coherent (7)
I believe the answer is:
logical
'coherent' is the definition.
(I know that coherent can be written as logical)
This is all the clue.
(Other definitions for logical that I've seen before include "Showing rational thought" , "Correctly reasoned, makes sense" , "Well-reasoned" , "Clearly and soundly reasoned" , "Correctly thought out" .)