Myanmar, once (5)
I believe the answer is:
burma
'myanmar once' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for burma that I've seen before include "SE Asian country" , "Country whose name was changed to Myanmar in 1989" , "Old name for Myanmar" , "Country also known as Myanmar" , "Rumba (anag)" .)