1. In anatomy and zoology, a small opening or perforation; a window: In her medical book, Marie read that a fenestra could be in a bone, especially between the middle and inner ear.
2. A transparent spot in an otherwise opaque surface: An fenestra can be present in the wings of certain butterflies and moths.
3. Any opening resembling a window: Ssome plaster casts, surgical drapes, or surgical instruments.can have fenestrae.
4. In architecture, a window-like opening: While drawing the plans of a building, Lisa made sure that there were many fenestrae in the walls to let in as much light as possible.

A vein of the internal ear draining the region of the round window, which drains into the vestibulocochlear vein: The vena fenestra cochlea of the ear is also known as the round window or the vein of the the cochlear window