曇り空

1. Origins, structure, and basic meaning

• Structure: The compound 曇り空 (くもりぞら) joins cloudy conditions with 空 and names the overcast sky itself.
• Basic usage: It sets a scene in 曇り空の下 or serves as the visible subject rendered in a painting.

2. Common pitfalls and similar expressions

• The overcast sky itself
  • It is a noun for the visible sky, rather than merely the weather condition of being cloudy.