The invention of words is a tricky business in the creation of fantasy and science fiction. After all, if you give people a dozen new words to learn, they’ll quickly be overwhelmed, irritated, or both. That in mind, there’s a trick that most have seen but many misuse: You can borrow words in the common parlance and repurpose them.
Words like paladin, Templar, shaman, and covenant are all terms with fairly specific meanings in the real world. They refer largely to things that exist, and yet they are used otherwise in fiction so commonly that they have crept into the cultural typology. That is to say, they are applied so widely and broadly that they have become a word that’s up for grabs.
By using these sorts of words carefully, you can have a word that stands out as being a novelty in the world you’ve created without having to actually create a new word and risk its sounding silly or overwhelming the feeble mind of the reader.
To do this, though, you must ensure that there is a certain connection between your character, organization, or creature and the word that you’ve chosen. Calling a simple, vicious creature a paladin simply won’t work – paladin invokes holy violence, self-righteousness, and a crusader’s verve. It doesn’t need to be a good character, but it must have some element of the original. Similarly, Templar, referring to specific crusaders, serves a very near purpose, with (thanks to Dan Brown) a hint of conspiracy. Shaman, on the other hand, holds a very tribal meaning, and can thus be used to refer to something pseudo-human without much trouble. A creature just intelligent to develop tools and culture but not so intelligent as to warrant a diplomatic envoy or an attempt at cultural understanding can very easily become a shaman, particularly when it carries a spiritual connotation – whether that’s an ape, a robot, or a strangely formatted neo-wolf. For each term, there is a range of purposes that it can fill, broad but bounded.
To carry with you a sense of the word you wish to borrow and to apply it judiciously and in such a way as to ensure that the new evokes the old is a technique that can save a piece of speculative fiction. The key is just to be very, very careful how each one is used.