Describes a depressed, heavy mood or atmosphere. Often used in literary or somewhat formal contexts.
雨の日が続くと、鬱気な気分になりやすい。
When rainy days continue, it's easy to feel gloomy.
彼の顔には鬱気な表情が浮かんでいた。
A melancholy expression appeared on his face.
Compound of 鬱 (dense, depressed) and 気 (spirit, mood). The exact historical derivation is uncertain, but the kanji combination directly suggests a depressed state of mind.