空 （クウ） empty air, sky, shunyata (the lack of an immutable intrinsic nature within any phenomenon), emptiness, air force, fruitlessness, meaninglessness, void (one of the five elements), empty (e.g. set)

空域 （クウイキ） airspace

領空 （リョウクウ） territorial airspace

防空 （ボウクウ） air defense, air defence

空 （そら） sky, the air, the heavens, weather, far-off place, distant place, state of mind, feeling, (from) memory, (by) heart, falsehood, lie, somehow, vaguely, fake

空模様 （そらもよう） look of the sky, weather

定めなき空 （さだめなきそら） changeable weather

晴れた空 （はれたそら） clear sky, cloudless sky

開く （あく） to open (e.g. doors), to open (e.g. business, etc.), to be empty, to be vacant, to be available, to be free, to be open (e.g. neckline, etc.), to have been opened (of one's eyes, mouth, etc.), to come to an end, to open (one's eyes, mouth, etc.), to have a hole, to form a gap, to have an interval (between events)

空き （あき） space, room, gap, emptiness, vacancy, opening, empty seat, free time, time to spare, disuse, unused thing

空き缶 （あきかん） empty can

開ける （あける） to open (a door, etc.), to unwrap (e.g. parcel, package), to unlock, to open (for business, etc.), to empty, to remove, to make space, to make room, to move out, to clear out, to be away from (e.g. one's house), to leave (temporarily), to dawn, to grow light, to end (of a period, season), to begin (of the New Year), to leave (one's schedule) open, to make time (for), to make (a hole), to open up (a hole)

空 （から） emptiness, vacuum, blank

空手 （からて） karate, empty handed

もぬけの殻 （もぬけのから） completely empty (of a residence, etc.), vacant, deserted, body from which the soul has left, corpse, shed skin (of a snake, insect, etc.)

空く （すく） to become less crowded, to thin out, to get empty, to be hungry

空かす （すかす） to feel hungry, to get hungry

虚しい （むなしい） empty, void, vacant, vain, fruitless, futile, ineffective, lifeless