Foreign article includes untruth (5)
I believe the answer is:
alien
'foreign' is the definition.
(similar in meaning)
'article includes untruth' is the wordplay.
'article' becomes 'an' (indefinite article).
'includes' is an insertion indicator.
'untruth' becomes 'lie' (lie is a kind of untruth).
'an' placed around 'lie' is 'ALIEN'.
(Other definitions for alien that I've seen before include "Creature from another planet" , "exciting film based in space" , "Foreign, strange" , "Martian, say" , "Foreign - film directed by Ridley Scott" .)