Dangerous mount in Vietnam (4)
I believe the answer is:
etna
'dangerous mount' is the definition.
'Etna' can be an answer for 'mount' (Etna is an example). I'm not certain of the 'dangerous' bit.
'in vietnam' is the wordplay.
'in' says the answer is hidden in the clue.
'ETNA' can be found hidden inside 'vietnam'.
Can you help me to learn more?
(Other definitions for etna that I've seen before include "Volcanic mount in Sicily" , "Volcano in Sicily, quite neat" , "It can be scorching" , "It sometimes blows its top" , "Sicily's 15" .)