Terry,
No, you are using the word "primary" casually, but Primary Key is a formal relational database concept. You can read more about it at:
http://fox.wikis.com/wc.dll?wiki~PrimaryKey~softwareEng>With multiple indexes (or TAGs), each index (or Tag) would have a primary key, right? The primary key is the first "field" in the index key (example CUST+INVOICE, CUST is primary key).