A cloud.

The apparent arch, or vault, of heaven, which in a clear day is of a blue color; the heavens; the firmament; -- sometimes in the plural.

From the Indo-European base meaning 'cover', came the Anglo-Saxons word for sky, heofon 'heaven', in the 13th century. Eventually heaven was replaced by Old Norse sky 'cloud'.

The sky is the normal background texture. It consists in a blue sky with white clouds. A: Still sky in 1.2

The vault-like apparent surface against which all aerial objects are seen from the earth.

1. The apparent surface against which all aerial objects are seen from the earth. 2. Same as sky condition, sky cover, state of the sky.