It is also used extensively in the photographic world, for instance one may use photosensors to slave electronic flash units to a single master.
Changing the tags would require every OpenACS 4.x site in the world to change their custom source code when updating, which I imagine would make a fair number of people somewhat unhappy.
Here's a link to an entire engineering genre which makes extensive use of that terminology.
And here's a snippet from a dictionary:
"4. A machine or component controlled by another machine or component."
The other three entries refer to human slavery...
