: the amount that a container (such as a tank or cask) lacks of being full
First Known Use of ullage
15th century, in the meaning defined above
History and Etymology for ullage
Middle English ulage, from Anglo-French ulliage, from *ullier to fill a partially empty cask, from Old French (Picard dialect) oel bunghȯle, literally, eye, from Latin oculus eye — more at eye