'Immure' - (dictionary.com)
–verb (used with object), -mured, -mur·ing.
1. to enclose within walls.
2. to shut in; seclude or confine.
3. to imprison.
4. to build into or entomb in a wall.
5. Obsolete . to surround with walls; fortify.
A place where words and thoughts are confined. All other definitions are left to chance.