Lacuna
Part of speech: noun
Definition: A small opening; a small pit or depression; a small blank space; a gap or vacancy; a hiatus. An absent part, especially in a book or other piece of writing, often referring to an ancient manuscript or similar. A space visible between cells, allowing free passage of light.
Caisson
Part of speech: noun
Definition: An enclosure, from which water can be expelled, in order to give access to underwater areas for engineering works etc.The gate across the entrance to a dry dock.A floating tank that can be submerged, attached to an underwater object and then pumped out to lift the object by buoyancy; a camel.A two-wheeled, horse-drawn military vehicle used to carry ammunition (and a coffin at funerals).A large box to hold ammunition.A variant of coffer.