Coherent American serving in pub (7)
I believe the answer is:
logical
'coherent' is the definition.
(I know that coherent can be written as logical)
'american serving in pub' is the wordplay.
'american serving' becomes 'gi' (GI is a term for a US soldier).
'in' indicates putting letters inside.
'pub' becomes 'local' (one's local pub).
'gi' inserted within 'local' is 'LOGICAL'.
(Other definitions for logical that I've seen before include "having good reason" , "According with reason" , "entirely reasonable" , "Based on reason" , "clear" .)