carriwitchet is a new one on me, but certainly we are getting positively metaphysical over what is, to me at least, a simple matter of a word to express the opposite of the contents of a container; i.e., the non-contents.

That brings me to this question for everyone: I am sure I have, somewhere, seen a word which is an antonym for ullage, but I can't think of it. Can anyone? Uncommon word, like nonage, the antonym of dotage.