You can use miscellaneous functions in custom tables and fields. See Adding a New Custom Table and Defining and Editing Field Formula for further details. The Miscellaneous Functions category currently includes the lookup function.

LOOKUP(remote_table,remote_result_column,current_match_column, remote_match_column)
The Lookup function imports a field from one table into another table, by matching two other corresponding fields from both tables. The result will be the value in remote_result_column for which the corresponding remote_match_column equals the current_match_column.