Land bordered by the Mekong (4)
I believe the answer is:
laos
'land bordered by the mekong' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for laos that I've seen before include "Landlocked state in southeastern Asia" , "Mountainous state in southeastern Asia" , "South-east Asian republic, capital Vientiane" , "Republic of southeast Asia" , "part of Asia" .)