While this designation of "orders" instead of "levels" got edited out in the published product, I did find one place where the use of "order" in that context remained. Check out the monster entry for Dwarves (emphasis added):
I found this wording in my second edition copy of the rulebook as well as in my third edition of the basic book. I'm curious as to whether it stayed in subsequent versions of the book.For every 40 dwarves (or possibly fewer) there will be one high order dwarf, the leader, who may have magic arms or armor and be of level 2-7.
I never would have given this term a second thought if Zenopus Archives hadn't begun that detailed review of the Holmes manuscript. Since that was the rulebook that got me started playing D&D way back when, I'm always interested in reading more about it, and I'm happy to contribute to the knowledge regarding that tome in my own small way.