Vietnam neighbor (4)
'vietnam neighbor' 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 "Country of SE Asia" , "Republic of southeast Asia" , "Landlocked state in southeastern Asia" , "Indo-Chinese country" , "Country of Indo-China, capital Vientiane" .)
(Other definitions for cambodia that I've seen before include "Kampuchea before 1975" , "SE Asian nation" , "Country, part of Indochina under French rule until 1953" , "SE Asian country" , "SW Asian state" .)