South-eastern guard could be sweetened (7)
I believe the answer is:
sugared
'sweetened' is the definition.
(I know that sweetened can be written as sugared)
'south-eastern guard could be' is the wordplay.
'south' becomes 's' (abbreviation).
'eastern' becomes 'e'.
'could be' indicates an anagram.
'e'+'guard'='eguard'
'eguard' is an anagram of 'ugared'.
's'+'ugared'='SUGARED'
(Other definitions for sugared that I've seen before include "Sweetened" , "Sweetly coated (almond)" .)