It appears that these are your relationships:
Supplier::__pk_Supplier = Purchase::__fk_Supplier
If those are your relationships, you can put fields from PaymentTerms on your Purchase layout and they will display the desired data. You can also define either Calculation fields or data fields with auto-enter calculations that can refer to fields from PaymentTerms.
@PhilModJunk - Thanks!
After I read your post I figured out why it wasn't working for me... The way that I had my relationships setup, i didn't have a connected relationship that included all 3 tables, I had it split into two parts w/ 2 instances of the Supplier table on the Relationship view. My setup was:
Once I changed it and tied it all together, it worked.