空

racing (of an engine); idling; spinning (without grabbing; of wheels)

going round in circles (of an argument, discussion, etc.); going nowhere; being fruitless

off the top of one's head; from thin air

from memory

vacant land; unoccupied ground; empty lot

Go (game)

empty point

empty seat; unoccupied seat

vacancy; vacant post

karate

空手 only

being empty-handed; having nothing in one's hands

high in the sky

space; room; gap; emptiness

vacancy; opening; empty seat

Nouns which may take the genitive case particle 'no'

free time; time to spare

Nouns which may take the genitive case particle 'no'

disuse; unused thing

available room (hotel); vacancy; room to let

empty can

Abbreviation

air conditioning

sky blue

vacant house; unoccupied house

putting on a brave face; put-on cheeriness; pretending one is fine; show of courage; bravado; Dutch courage

mishearing

(feigned) deafness

homophonic translation of song lyrics for comic effect

dry wind

to cover up the sky (e.g. smoke)

air force

Colloquial

atmosphere (esp. of a place or person); mood; vibe; ambience

air-raid

Abbreviation

aircraft carrier

airspace

empty nest

empty house; empty home

Abbreviation

burglary (of an empty house); burglar (who targets empty houses); sneak thief; prowler

vacant land; unoccupied ground; empty lot

apprehensive; vaguely fearful; gloomy (about the future); somewhat alarmed