空

demanding payment for a non-existent loan

vacuum fluorescent tube

perfectly clear and serene sky

Noun or verb acting prenominally

air cooling

conventional aircraft carrier (i.e. non-nuclear)

seismic gap

aviation insurance; aerial insurance

hub airport

air conditioning unit; AC unit; air conditioner

visuospatial agnosia

vacuum cooking; sous vide

air dose rate (esp. radioactivity)

perfect vacuum

Anatomy

potential space

spatial gradient

Mathematics

simply-connected space

cavity resonator; microwave resonance cavity; rhumbatron

pneumatic drill; air drill

Chemistry

mixture of air and hydrocarbon gas or vapour

utopian

fictitious assets

aircraft engine

glossy abelia (Abelia grandiflora)

man-portable air-defense system; MANPADS