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.

The opening into the duodenum made by the common bile duct and the pancreatic duct.

A small, rounded, recessed opening in the medial wall of the tympanic cavity: The fenestra cochlea is located behind and below the fenestra vestibuli, under cover of the projecting edge of the promontory and communicating with scala tympani of the cochlea from which it is separated by the secondary tympanic membrane.

The two window-like, membrane-covered openings between the middle and the internal ear: Janet's ear was aching quite a bit, and after her condition was examined, her otorhinolaryngologist said that ithe disorder was located near the fenestra ovalis and could be treated.

A membrane-covered opening between the middle and inner ears in amphibians and mammals through which energy is sent after traveling in the membranous labyrinth: The fenestra rotunda is a small opening, especially either of two window-like apertures in the medial wall of the middle ear.

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