Verb (5-dan, る, intransitive)
1. to get cloudy; to cloud over; to become overcast
その向こうに見える空は少し曇り始めていた。The sky visible beyond that was beginning to get a little cloudy.
2. to cloud up; to fog up; to mist up; to become dim
それは窓を少しだけ曇らせ、視界を白く遮りました。It fogged up the window slightly, blocking the view with white.
3. to be gloomy; to be clouded (expression); to be downcast
いつも輝いている笑顔が今日はすっかり曇っている。The smile that is always shining is completely clouded over today.
4. to look slightly downward (of a noh mask; indicating sadness, grief, etc.)
from 面曇る