See eye to eye in Gretna Green (5)
I believe the answer is:
agree
'see eye to eye' is the definition.
(if two people see eye to eye they agree on things)
'in gretna green' is the wordplay.
'in' indicates a hidden word.
'AGREE' can be found hidden inside 'gretna green'.
(Other definitions for agree that I've seen before include "suit" , "Shake on it" , "Concur, acquiesce" , "Arrive at a settlement" , "See eye to eye" .)