headspace

• head space, head-space

head +‎ space

headspace (countable and uncountable, plural headspaces)

1. The space between the top of the contents of a container (such as a jar) and its seal (such as a lid).

   Synonym: headroom

   • 1997, S. D. Holdsworth, “Food Preservation Processes”, in M. D. Ranken, R. C. Kill, C. Baker, editors, Food Industries Manual‎, 24th edition, Blackie Academic and Professional, →ISBN, page 517:

     Control of headspace is important for economic and technical reasons. Underfilling will contravene Weights and Measures legislation and may cause rusting in the headspace […]

2. (informal) One's mental state.

   Synonym: brainspace

   • 1996, Andrew Cowan, Common Ground:

     It's like, I need to clear my headspace but I can't do that with him around because he's just ego, you know? He dumps on me. So that's it.

3. (informal) Unscheduled time for reflection and thinking.
   • 2011, Eric J. Gregory, Would You Like Profits, →ISBN:

     As a business owner, a truly effective business owner that is building a profitable business machine, you need headspace, thinking time, planning time, brainstorming time, education time, decision making time, questioning time and more thinking time.

4. (firearms) The gap between the face of the bolt and the stopping surface for the cartridge.
5. (chemistry) The gas phase in contact and in equilibrium with a nonvolatile sample.

headspace (third-person singular simple present headspaces, present participle headspacing, simple past and past participle headspaced)

1. (firearms) To occupy a headspace.

• spacehead