It splits up the levy (5)
I believe the answer is:
'levy' is the definition.
(I know that tithe is a type of levy)
'it splits up the' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'splits up' becomes 'i' (I can't justify this - if you can you should believe this answer much more).
Can you help me to learn more?
(Other definitions for tithe that I've seen before include "property tax" , "Gift of tenth" , "One-tenth; church tax" , "Charge" , "Tenth of income given to church" .)