Derian, pl. deriani
It’s a very old Cortiian word, and it literally means ‘rider’. It’s also, in wider use, a generic title for any Cortiian, rather like ‘citizen’ in the Federated Planets Alliance.
The legend goes something like this; back in pre-spaceflight history, all Cortiians fought from horseback. Depending on how much of a conspiracy theorist you are, you might see the connection to the Earth traditions about ‘nightmare’ and any number of the old Celtic legends about a mounted hunt. (See First Colonial Fleet.)
In actual point of fact, reliable rumour and Cortiian archives indicate that that’s a lovely piece of romanticism, and about what a Central Worlds historian would come up with. The original Cortii were a mercenary troop (making them, incidentally, the longest-operating mercenary force in human space), and they fought from whichever angle gave them the best advantage. If the shock and awe approach was needed, they would probably have sent in a mounted charge. On the other hand, try sneaking into a fortification on horseback.
However, as spaceflight became increasingly part of everyday life, space, ironically, became a luxury. Space constraints on the Central Worlds planets, which became overpopulated in typical humanoid style before the advent of population-wide contraception and the First Colonial Fleet, made keeping large animals of any kind expensive. Space on stations, less of a problem in itself, but the volume of clean air required provides its own constraint. Spaceships – while those not built to make planetary re-entry can be basically any size and shape you want, larger typically increases mass, which is what a drive moves…you get the picture.
Horses became a rarity.
In fairly short order, after the First Sector War, several of the human governments decided that putting some brakes on the Cortii would be a good idea, and forbade recruiting, denied Cortiians interstellar citizenship, and otherwise tried all and any methods short of direct confrontation (which had been proven not to work very well).
Given that by this point, the Cortii had a range of footholds across humanoid space, they declared themselves a separate category of humanoid (see genetic adaptation), and managed to argue that into law as a basis for self-governance.
At about this point, the Councils began pushing the use of horses again. As a self-governing sub-species with multiple interstellar settlements, they now had the additional cachet of being a taboo topic in polite society. A few highly visible actions including full mounted units set off a rash of artwork, interactive entertainment shows, educational programming, etc., that did a much better job of recruitment than any formal campaign ever would have, and the Cortiian governing body (the Councils), chose ‘derian’ as their appellation of choice.