Not exactly, it doesn't look like the definition or even connotations of "ineffable" include "unknown".

It does in the sense that ineffable things are unable to be described in language (conceptually: unknown to language).

Anything that is known can be described in language by giving it a name.

Hey, that's today's smbc https://www.smbc-comics.com/comic/r The problem is, there's no good reason to think the concept of 彊 in your mind is at all similar to the concept of 彊 in my brain. After all, we (probably) don't pronounce it the same, right?