Primary/Secondary aka Master/Slave already happened with DNS... e.g. http://www.zytrax.com/books/dns/ch4/ http://www.zytrax.com/books/dns/ch4/ and since you can

Primary/Secondary aka Master/Slave already happened with DNS... e.g. http://www.zytrax.com/books/dns/ch4/ http://www.zytrax.com/books/dns/ch4/ and since you can have Master-Master relationships in databases as well as "equal" relationships where two masters can each be slaves to the other for redundancy... it's messed up however you look at it. Personally I prefer Primary & Secondary but I'll use the language the manual uses for whatever product I'm configuring, since it makes life easier.