sky; the air; the heavens
The physical sky or the space above; also used in poetic or literary contexts for the heavens.
The sky is beautifully clear.
Birds are flying in the sky.
Used in expressions like 空模様 (weather conditions) or 空が怪しい (the weather looks threatening).
The weather is gloomy today.
far-off place; distant place
Often used in set phrases like 空の果て (the ends of the earth) or 空遠く (far away).
He set off for a distant land.
Appears in the pattern 〜空もない, meaning 'too preoccupied to notice anything else'.
She's fallen in love and has no mind for studying.
from memory; by heart
Used adverbially as 空で, meaning 'by heart' or 'from memory'.
He can recite a long poem from memory.
Used in compounds like 空言 (そらごと, lie) or 空頼み (false hope). Rarely used alone.
That's nothing but a lie.
Prefix-like use before adjectives, expressing a vague or uncertain feeling.
It's a vaguely frightening story.
fake; pretended
Prefix-like use before nouns or verbs, indicating something false or pretended.
He tried to gain sympathy by fake crying.
He looked up at the starry sky and sighed.
In the afternoon the sky cleared and blue sky appeared.
The sky started to cloud over in the evening.
An airplane is flying through the sky.
I'm so busy I don't even have time to eat.
空 is the plain, everyday word for the physical sky, whereas 虚空 is more literary and can also mean an abstract, metaphysical void.
wide open sky; the heavens; firmament
seeing something that isn't there; hallucination · pretending not to see; turning a blind eye · looking upwards; upward glance
mishearing; auditory illusion · feigned deafness; pretending not to hear · homophonic translation; mondegreen
beautiful sky
sky blue
cloudy sky; overcast sky
inattention; absent-mindedness; spacing out
look of the sky; weather; sky conditions
wintry sky; cold winter weather
body; one's fortune
autumn sky; clear blue autumn sky
evening sky; twilight sky
rainy sky; threatening sky
winter sky
New Year's morning sky
summer sky; summery weather; clear blazing summer weather
morning sky
fabrication; falsehood; lie
accidental resemblance
fabricated dream; made-up dream
feigned sleep; playing possum
boxed lunch sold at airports
arching backward; looking up
crocodile tears; fake tears