1. A place with a lot of crisscrossing or complicated passages, tunnels, or paths in which it would be easy to become lost.
2. An intricate structure of interconnecting passages through which it is difficult to find one's way; a maze.
3. Something which is made up of many different parts that is complicated and hard to understand: "They tried to figure out a labyrinth of tax regulations."
4. A structure consisting of connected cavities or canals, especially the inside of the ear.
5. The internal or inner ear, composed of the semicircular ducts, vestibule, and the cochlea.
6. Any group of communicating cavities, as in each lateral mass of the ethmoid bone.

Ethmoid bone: an irregularly shaped, spongy bone that provides the floor of the front part of the skull and the roof of the nose.

The ethmoid bone consists of two masses of thin plates enclosing air cells and looks like a sieve.