Foreign article includes falsehood (5)
I believe the answer is:
alien
'foreign' is the definition.
(synonyms)
'article includes falsehood' is the wordplay.
'article' becomes 'an' (English indefinite article).
'includes' means one lot of letters goes inside another.
'falsehood' becomes 'lie' (lie is a kind of falsehood).
'an' going around 'lie' is 'ALIEN'.
(Other definitions for alien that I've seen before include "Stranger" , "coming from overseas" , "Foreign, strange" , "Outlandish" , "24a [ESTRANGE]" .)