Vapour

A cloud is an accumulation of water vapour in the sky.

Vapour ascends from water. From it is formed a cloud, and mist near the Earth.

Thunder is made from a sulphurous vapour, breaking out of a cloud with lightning, thundering and striking with lightning.

The breath of my horse formed vapour in the frosty air.

All liquids when heated give off vapour, the amount increasing as the temperature rises.

It's water vapour.