airspace

IPA: ˈɛrspeɪs

(politics, aviation) A specified portion of the atmosphere, especially that under the technical aviation control and/or jurisdiction of a particular state over which territory (and territorial waters) it lies.
(aviation) that part of the sky designated for the sole use of aircraft.
(broadcasting) Space (i.e. a few neighboring frequencies) available for broadcasting within a particular frequency band.
The portion of an enclosed area which contains air, especially breathable air.
(construction) The cavity in a cavity wall containing air for insulation.

air space

IPA: ˈɛrspeɪs

Alternative spelling of airspace [(politics, aviation) A specified portion of the atmosphere, especially that under the technical aviation control and/or jurisdiction of a particular state over which territory (and territorial waters) it lies.]