There's an article about it for tax (5)
I believe the answer is:
tithe
'for tax' is the definition.
(historical tax paid to the church)
'there's an article about it' is the wordplay.
'there's an article' becomes 'the' (the definite article).
'about' means one lot of letters goes inside another.
'the' going around 'it' is 'TITHE'.
(Other definitions for tithe that I've seen before include "that was given to clergyman" , "Tenth part paid to a church" , "10 per cent levy" , "Levy, originally worth one tenth" , "One tenth - old church tax" .)