Article new at that time (4)
I believe the answer is:
then
'at that time' is the definition.
('then' can be a synonym of 'at that time')
'article new' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'new' becomes 'n'.
'the'+'n'='THEN'
(Other definitions for then that I've seen before include "soon?" , "At that time; next" , "Once upon a time" , "Subsequently - previously" , "Afterwards - as a result" .)