sky

The atmosphere above a given point, especially as visible from the surface of the Earth as the place where the sun, moon, stars, and clouds are seen.

With a descriptive word: the part of the sky which can be seen from a specific place or at a specific time; its climate, condition, etc.

(chiefly literary and poetic, archaic) Usually preceded by the: the abode of God or the gods, angels, the souls of deceased people, etc.; heaven; also, powers emanating from heaven.

Ellipsis of sky blue.

(mathematics, theoretical physics) The set of all lightlike lines (or directions) passing through a given point in space-time.

(obsolete, informal, rare) In an art gallery: the upper rows of pictures that cannot easily be seen; also, the place where such pictures are hung.

(obsolete) A cloud.