This has the potential of getting ugly, and perhaps I should ask a linguist instead of the lore, but...

It surely surprises nobody that the term 'crusader' is related to 'crusade', the name history has given the homonym medieval expeditions and military campaigns. It's http://en.wikipedia.org/wiki/Crusades#Etymology_and_usage clearly points to the name coming of course of course from 'cross', the symbol of the Christian faith.

I'm not trying to take a stance for political correctness or anything like that, but I'm wondering if the term 'crusader' does fit into the TES setting, since I don't know of cross symbology in it (I don't know much about any of its symbology I'm afraid). I do recall the http://en.wikipedia.org/wiki/Ankh symbol appearing in Arena, possibly Daggerfall, so perhaps it kind of links to that.

But for the Nine Divines, for which the archfamous 'Divine Crusader' was fighting, the symbol is a red diamond or rhombus. Wouldn't it be more fitting to name a warrior devoted to their cause a... 'rhombader'? Sounds a tad silly, maybe someone who can mix geometry and linguistics better can come with something more palatable. Perhaps something with a -nit or -nite suffix would be better, like Zakarumites of the Zakarum faith in Diablo.

Or would trying to find a fitting title for such other symbols be pointless due to ridiculousness or the publics unfamiliarity?

Needless to say I hope this can stay away from RL religious discussion. If not, I'm sorry for having overstepped.

Despite its etymology, the word crusade means to take part in a campaign concerning a political or religious issue. Therefore it fits perfectly.
It's a well recognized word with a lot of significance behind it, and people can instantly understand how it applies to a character.
If they used "rhombader" no one would take the plot seriously.

Why invent a new word when there's a real one that fits perfectly? For example, an outspoken Environmentalist who is involved in a campaign can be called a crusader... Not a Enviro-rader.

Yes of course, the words crusade, crusader and derivatives have had a long time to evolve and adapt to everyday use, and is fitting in a lot more settings than just religious ones. But strictly speaking, unless I'm mistaken about this as well, its origin is in 'cross', the Christian one. Hence the thing is, and I should have mentioned it, I'm not sure how it could have even come to be in TES to begin with.

Of course one could argue that the Tamrielic language as a whole sounds suspiciously similar to English... as in, perhaps it doesn't make much sense to discuss what term they would use for what we would have no choice of translation other than 'crusader'. Could it be the same as wondering what we would call an outspoken person heavily invested in a campaign before our RL Crusades?

http://tvtropes.org/pmwiki/pmwiki.php/Main/TranslationConvention is in effect. The etymology of the word is irrelevant as despite English being the language we hear, it is not the language the characters are speaking.

You could make etymological arguments against almost anything in Tamriel, as the world and cultures are alien to our own. Like the above posters already mentioned, it's conveniently translated for you into a familiar form.

Making stuff up:

The cross actually is found in Imperial iconography. There are two widely used explanations for this. Neither of them is related to the crucifix of our world, as Tamrielics never executed anyone that way (they're not barbarians!). The first is that it is a representation of a rhombus or a kite, the Imperial Diamond, but shown with its diagonals rather than its edges. The second, which is related, is that it is a stylized skeletal torso - a spine, and a collarbone or ribcage across it. This represents the Colovian "spine" that encloses the sensitive organs of Nibenay.

Or a symbol of the sword as in the lessons:

The link between the crusader and the cross is really important in the ES - but only known by a few.

In a http://www.gamesas.com/topic/1455044-the-zero-sum-of-zhiro/I point some of the facts about this.

The most important part (and in fact nearly sole mention of the cross) comes from the 36 Lessons :http://www.imperial-library.info/content/thirty-six-lessons-vivec-sermon-thirteen

This is when Vivec is describing how the secret door (probably for the Amaranth) is created. The sword must be at the center for this (7).

Vivec says himself he is the sword, but a lot of things let think it was only true at the time of the Sermons. His tribunal/Triune hous is no longer active, even before the Death of Almalexia ans Sil. He doesn't have spoke, which should be keeping the center from the fall of the house of trouble (4) from the 5 corner of the world. 4.5, might be landfall (we will see?)

But Vivec, when he began, was a sword, a cross. And he has his crusaders ; some ordinators , and some of the buoyant armiger, who also have this class. Of course, these crusaders are the best http://www.uesp.net/wiki/Morrowind:Ralyn_Othraveland http://www.uesp.net/wiki/Morrowind:Mertis_Falandas.

So, it seems the crusaders have the role of keeping the "sword at the center".

It is interesting to see that Skyrim mentions that blades come from akaviri (must be tsaesci) http://www.imperial-library.info/content/book-dragonborn, as these tsaesci seem to have come to reman in order to protect him as dragonborn, and also as keeper of the Dragon fires (Pelinal also, as a crusader, helps a Dragonblood : Alessia, and thus gain the Convenant with akatosh for the Dragon fires). And then, tsaescis made all they can to be http://www.imperial-library.info/content/remanada, who is probably the actual - and final for the Amaranth - sword at the center, as talos is clearly at the center, supported by his "spokes", the 8 other aedra, and prevent Mundus from destruction.

The "magic cross" can also be tied to the Crux of Transcendence, the Heart or Mantella; suffering for godhood. In this sense, the crucifix and the gallows are very similar symbols.

I do like the way you connect the cross and the crusaders via the Tsaesci, Sifrael; Hrol's "Questing Knights" are certainly one sort of Crusade.