Spew black lies, oddly about Switzerland (5)
I believe the answer is:
belch
'spew' is the definition.
(thesaurus)
'black lies oddly about switzerland' is the wordplay.
'black' becomes 'b' (abbreviation as in pencil classifications).
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
'about' says the letters should be written backwards.
'switzerland' becomes 'ch' (short for Confoederatio Helvetica, its Latin name).
The alternating letters of 'lies' are 'le'.
'le' reversed gives 'el'.
'b'+'el'+'ch'='BELCH'
(Other definitions for belch that I've seen before include "Eructation" , "Expel gas through the mouth" , "Emit wind or smoke" , "Eructate" , "Expel (smoke) forcefully" .)