I think what you’re looking for is one list and then that list is referenced by both tables, the Ingredients Table and the Order Date Table. If I’m wrong, please say so and I’ll try again.
My approach would be to create a third table that is just Units. This can be a one column table that lists the units you will be using throughout the document. Then in your other two tables, change the column format to “Lookup from Table” and choose the Units table. This will give the same feature as the select list, but will refer to the new Units table for the values. If you change or add values in the new Units table, everything will transfer and change everywhere else in the document!
More on Lookups here:
Using Lookups
There is another option that might work where units added to one will auto-populate the other:
Add new values to select list or other table from row input
Again, if this is not what you’re looking to do, let me know and I’ll give it another try!