This is an irregular feature - both in frequency and oddness - dedicated to a word I came across that I have never previously used.
ullage (UH-ledge) adj. The unfilled space in a barrel, cask, or wine bottle.
The word is most recently derived from the French word ouiller , meaning "to fill a barrel up to the bunghole." Ullage can trace its roots back to the Latin oculus ("eye"), the word that Romans used to describe the bunghole of a barrel.
No Beavis and Butthead references, please.