Dropdown List with different display name and values

When I create a dropdown list I’d like to have different names when choosing an option than their actual values.

For example, when I click on the drop down list I get the following options:

  • Direct Federal Tax Law
  • Cantonal Tax Law

When I then choose one it shouldn’t insert the whole name in the field but rather only the abbreviation. So when I choose Cantonal Tax Law it should insert CTL into the field.

How can I specify this?

In advance many many thanks for your help.