Covered with or characterised by clouds; overcast.
"The sky turned completely cloudy just before the storm arrived, blocking out all sunlight."
In plain English: Cloudy means when the sky is covered with so many clouds that you can't see the sun clearly.
"The sky turned cloudy just before the rain started."
Usage: Use "cloudy" to describe weather that is overcast with clouds or liquids containing suspended particles that make them opaque. Avoid using it for dark skies without visible clouds, which should be described as cloudy only if the cloud cover is present.
The word cloudy comes from the Old English term clūdiġ, which originally meant stony or rocky rather than referring to overcast skies. Its modern sense of gloomy weather developed later in Middle English when it was formed by combining the noun cloud with the suffix -y.