空

Physics

air shower

atmospheric electricity

pneumatic tube

tea served without sweets

empty house; empty shop

Colloquial

fear of having blank days (e.g. for a freelancer); fear of not having anything planned

embossing; inkless stamping

vacant constituency

Archaic

type of loom used in olden times

loom; traditional loom

air conditioning

air dose (esp. radioactivity)

landing fee

Computing

null string

aerial inspection

coming untied

Mathematics

space-filling

air-raid

Buddhism

Kumuhensho; lowest heaven of Mushikikai; realm of non-form

stalled session of the Diet (Japanese Parliament)

touching a food with one's chopsticks, then removing them without taking it (a breach of etiquette)

atmospheric oxidation; oxidation upon exposure to the air; air oxidation; smoothering

airport (rail) station

paratroopers

air liaison officer