What's a something-in-ordinary?

Just watched “Jonathan Strange and Mr. Norrell” and at one point Strange claimed to be the British Army’s “magician-in-ordinary.” Now obviously that’s a fictional title, but it seemed like it was supposed to evoke something real.

It’s not easy to do a search on “-in-ordinary,” but I did discover that there is an office called “chaplain-in-ordinary,” but I can’t seem to find something that explains what the “-in-ordinary” part actually means.

So, any ideas? What is the meaning of the “-in-ordinary” part of a title that takes the form “[job, position, or office]-in-ordinary”?

Lazy answer, but Wikipedia actually has a pretty good write-up.

In particular:
*In relation particularly to the staff of the British Royal Household, and more generally to those employed by the Crown, it is used as a suffix showing that the appointment is to the regular staff, for example a priest or chaplain-in-ordinary, or a physician-in-ordinary, being a cleric or doctor in regular attendance. The usage goes back to the 17th century. *

Basically, what it means is that the person is appointed to be in regular physical attendance, not just associated - IRL, physicians-, painters-, chaplains-in-ordinary were expected to be part of the court, not just called on when their services were explicitly needed.

Gotcha. Cool, thanks’