Tax — it's included in article (5)
I believe the answer is:
tithe
'tax' is the definition.
(historical tax paid to the church)
'it's included in article' is the wordplay.
'included in' is an insertion indicator.
'article' becomes 'the' (the definite article in English).
'it' placed into 'the' is 'TITHE'.
(Other definitions for tithe that I've seen before include "10% tax" , "that was given to clergyman" , "Tenth part (as tribute)" , "One tenth - old church tax" , "One-tenth of income paid to church" .)