ullage

From Middle English ulage, from Anglo-Norman ulliage, from *ullier (“to fill a partially empty cask”), from Old French oel (“bunghole", literally, "eye”), from Latin oculus (“eye”). See French ouillage.

ullage (countable and uncountable, plural ullages)

1. In a wine bottle, the empty space between the cork and the top of the wine.
2. In a cask or barrel, the empty space, occupied by air, that is created by not completely filling the cask or barrel.
3. The topping-up of such a barrel with fresh wine.
4. In an industrial setting, the empty space in a tank, such as for fuel.

ullage (third-person singular simple present ullages, present participle ullaging, simple past and past participle ullaged)

1. To gauge the amount of empty space between the top of a cask and the level of liquid inside it.