Foreign article admitting fabrication (5)
I believe the answer is:
alien
'foreign' is the definition.
('alien' can be a synonym of 'foreign')
'article admitting fabrication' is the wordplay.
'article' becomes 'an' (indefinite article).
'admitting' is an insertion indicator.
'fabrication' becomes 'lie' (I've seen this before).
'an' placed around 'lie' is 'ALIEN'.
(Other definitions for alien that I've seen before include "coming from overseas" , "repugnant" , "Someone from outer space?" , "Foreigner, outsider" , "Otherworldly" .)