In Vietnam, a lively country (4)
I believe the answer is:
mali
'country' is the definition.
(Mali is an example)
'in vietnam a lively' is the wordplay.
'in' indicates the answer is hidden within the clue.
'MALI' can be found hidden inside 'vietnam a lively'.
(Other definitions for mali that I've seen before include "Send mail out to Africa" , "African state's" , "African country, once French Sudan" , "W. African country" , "African country, former French colony" .)