What is another word for brain casing?

There isn't a single, commonly used synonym for "brain casing" in the way you might be thinking. The term itself isn't very common or precise. It likely refers to the protective structures surrounding the brain, which could mean:

* Skull: This is the bony structure that encases the brain, offering the most literal protection.

* Cranium: This is a synonym for skull, emphasizing its dome-like shape.

* Meninges: These are the three layers of protective membranes that surround the brain and spinal cord.

* Dura mater, arachnoid mater, pia mater: These are the individual layers of the meninges.

So, the best "synonym" depends on what you are specifically trying to convey. If you are talking about the bone, "skull" or "cranium" is the most appropriate. If you are talking about the membranes, "meninges" or the individual layers are better choices.

If you can give me more context about what you are trying to say, I can give you a more accurate and specific answer.