In technology, the "master" controls one or more devices known as the slave(s). For the novel I am writing, I prefer avoiding the connotation of Master/Slave. Is their a word, term or other phrase that depicts this relationship more eloquently?
There was some controversy over this back in 2003 when Los Angeles Country asked manufactures/suppliers to stop using it.
This ultimately led different software platforms (like Drupal) to adopt, in 2014, the terms:
Other possible phrases that I like include:
For more information: http://en.wikipedia.org/wiki/Master/slave_(technology)
Please provide more information about the relationship you want to describe better in your question instead of just saying "replace Master/Slave".
There are some situations where Manager/Worker works. I find the comparison between real slavery and modern day economic "slavery" interesting. This is where workers are economic "slaves" to economic "Masters". For that reason, you may wish to avoid this too.
Some situations author/replica may work where the replica is nearly/completely read-only. This could be the case where the author is the only one able to record data, and does not respond to read requests (except from the replica using a different method). The replica is the one able to respond to read request, but cannot record data.
Server/Client is interesting as the authoritative one is recognized as have the purpose of serving the client's needs while maintaining authority. Think of a server in a food establishment refusing to sell alcohol to a minor. They are there to serve the client but only within certain limitations.
Some situations warrant a Primary/Secondary relationship like Microsoft Domain controllers, back in the day, the first Domain Controller was authoritative and handled nearly everything. Secondary Domain Controllers handled portions of the work in a semi-authoritative role much like a President and Vice President. The Secondary could be assigned certain authoritative roles by the Primary. Which introduces a President(P)/Vice-President(VP) relationship.
Immortal/Mortal is an interesting idea too. Obviously the religious context may limit the application. It's interesting to contemplate in regards to technical implementations. You could for example look into the relationship of Rancher (classic Cattle version) servers to Docker containers. The containers are temporal and can be replaced easily. The Rancher server is an orchestrator and really should be "immortal" for the system to continue running. Which leads us to a Rancher/Cattle relationship.
Perhaps Rancher/Cattle would be an acceptable replacement to describe the relationship if you are dealing with something like mages and "normal" humans. Or Super/Normal.