Foreign article contains untruth (5)
I believe the answer is:
alien
'foreign' is the definition.
(similar in meaning)
'article contains untruth' is the wordplay.
'article' becomes 'an' (indefinite article).
'contains' means one lot of letters goes inside another.
'untruth' becomes 'lie' (lie is a kind of untruth).
'an' going around 'lie' is 'ALIEN'.
(Other definitions for alien that I've seen before include "coming from overseas" , "Little green man, perhaps" , "Belonging to a foreign country" , "One is from outer space, perhaps" , "Foreigner, outsider" .)