Nice term, Shadow World.
This is probably too late, but ishim is a good, canonical Vilani word for what we think of as "shadow", as in ishimkarun, the shadow (lit. hidden) emperor. Note the Anglic translation is shadow, i.e. covert, even though the Vilani term simply means 'hidden'. There's some idiomatic translation going on that I wasn't aware of.
Next, we need a good-sounding complement for ishim -- either the conceptual "gerek" as you suggest, or the concrete "sigere". Both come from the same verb 'ger', to chart or map. I think your choice is good.
So, how about "Ishimgerek" -- "hidden world" literally, but in translation is more like "shadow world". Double meanings are also present: hidden chart, hidden map, shadow chart, or shadow map. Has a nice ring to it.
This implies that where in English we use "shadow" as an idiom of mystery, the Vilani do not.
But, that implication could be wrong, so I think you're free to use "Gerek Daar" or "Daar Gerek" if you like.
Well, I'm sure I'm going straight to Grammar Police Hell for this, but shouldn't it be "Daar
san Gerek" ... "daarsan" being the adjective form of the noun "daar?" Another possibility might be "Daargi Gerek" ("World of Shadow?"), if I'm reading your primer's description of the genitive case correctly.
But wait. There's more:
If we start from the basic idea of the Vilani as a society that highly values consensus and stability, then I think it's possible to see how
both "ishim" and "daar" can be used, but with strongly different results.
Thanks to your excellent dictionary, I see that "ishim" isn't just "shadowed," but also "screened." "Vetted," I think, would be another good synonym. This speaks towards the Vilani ideal of consensus -- to make something "ishim" (hidden, but screened) requires agreement of the group. It may or may not be pleasant for a thing to be declared "ishim;" but at least the Vilani would regard the condition as having been achieved legitimately.
"Daar," on the other hand, speaks more concretely to an actual shadow. It is obscured, but not as a mutually agreed upon state; instead, it just
happens. This may not matter when discussing something as simple as a shady tree or a sundial; but when describing a social or political entity, a Vilani might regard something that is "daarsan" as illegitimate, prurient, or even worse. In this sense, then, the terms "occult" or "occulted" serve as very good Anglic synonyms for "daar."
A Solomani might ignore the distinction between "ishim" and "daar," and think of
anything hidden as being inherently mysterious. A Vilani would respond that, no, it's not the darkness itself that concerns him, but whether or not society gave it permission to be there in the first place.
And so we can have two words for "shadow emperor:"
Ishimkarun (the agreed ruler of the universe), and
Daarsan Karun (something far less admirable). A rogue warlord or rebel leader, perhaps? or an underworld kingpin? Perhaps it represents a quasi-demonic mythical agent of chaos, or maybe even an
Ishimkarun so incompetent or depraved that he/she had to be declared "daarsan" and forcibly removed.
"Daarsan Gerek," then,
is a good euphemism for the Vilani Black Market (such as it is). Although it might more properly refer to criminal enterprises in general, or maybe even some really reviled (but necessary) Vilani caste.
The related word "Ishimgerek" seems a little more complicated; but I'm leaning towards "Imperial Court" as being one of the definitions.
