Learner's definition of SKY
: the space over the Earth where the sun, moon, stars, and clouds appear
a starry sky
the night/desert sky
There wasn't a cloud in the sky.
Dark clouds moved quickly across the sky.
Hailstones suddenly fell out of the sky.
The sun/moon was high in the sky.
The forecast is for sunny/blue/gray/overcast skies tomorrow.
partly cloudy skies
praise (someone or something) to the skies
take to the sky/skieschiefly US