Anger
noun
An angry energy comes out of you when you have anger.
怒気 looks simple, but it's a pretty advanced term more commonly used in literature, typically to describe a character's anger as expressed through their voices, facial expressions, attitudes, or the surrounding atmosphere.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
「よくそんな冷たいことが言えるよな！」と、コウイチは怒気をおびた声で言った。
"What a heartless thing to say!" said Koichi with anger in his voice.
相手は、こちらの怒気を感じたのか、急に静かになった。
The other person suddenly grew quiet, perhaps sensing my anger.
なんとか怒気を隠そうとしたが、引きつった笑顔しか作れなかった。
I tried to hide my anger, but could only manage a strained smile.
彼の鼻の穴は怒気を含んで膨らんでいる。
His nostrils swelled with anger.