One for example in southeast blockade (5)
I believe the answer is:
siege
'blockade' is the definition.
(I know that siege is a type of blockade)
'one for example in southeast' is the wordplay.
'one' becomes 'i' (Roman numeral).
'for example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'in' is an insertion indicator.
'southeast' becomes 'SE' (synonyms).
'i'+'eg'='ieg'
'ieg' going within 'se' is 'SIEGE'.
(Other definitions for siege that I've seen before include "Act of surrounding a town or fortress" , "Offensive encirclement" , "Persistent attempt to gain" , "Military operation surrounding a town" , "Operation to capture a fort, for example" .)