The term "sobornost" is used by Eastern Orthodox theologians, especially Russian Orthodox theologians, in much the same way that Roman Catholics use the word "catholic." It does not translate readily into English.
In the Russian version of the Nicene Creed, the word "sobornyi" is used where "catholic" (note the lower-case) is used by the Western Church: "one, holy, sobornyi, and apostolic church."
Western Christians would translate "catholic" in this context to mean "universal". Eastern Christians would translate sobornost in this context to mean something like "according to the whole."
In the East, this word takes some flavour from the unity of bishops, who, when they gather and all believe/proclaim the same thing at the same time, are embodying a sort of sobornost.
The word is variously translated in ecclesial documents: communion, unity, conciliarity.
I think that not every word is translatable from every language into every other language ... and this is one of them.
