Unless you are going to port you application to SharePoint, it is a good
idea to avoid multi-value fields. You have discovered one of the reasons
why. Instead, build a table with the Abbreviations as a Key, and the
description as a value, and you can use a table with a single row for each
value, and a subform to display both.
You can change the RowSource of the combo box that displays the field to a
query that includes the description field from the underlying table, change
its ColumnCount from 1 to 2, change the ColumnWidths property to provide a
width for each column, and change the ListWidth property if necessary so
that it's wide enough to show all the displayed columns.