Lacuna

noun

1. A small opening; a small pit or depression.
2. A small blank space; a gap or vacancy; a hiatus.
3. An absent part, especially in a book or other piece of writing, often referring to an ancient manuscript or similar.

   "Long lacunae in this inscription make interpretation difficult."

4. Any gap, break, hole, or lack in a set of things; something missing.
5. A space visible between cells, allowing free passage of light.