Warning, Advice, Caution
noun, verbal noun, の adjective
When you announce something to warn somebody, you're warning them. Sometimes you're just trying to give them some helpful advice.
けいこく
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
なんか警告文が出てきたんだけど…どうしよう？
I got some kind of warning message... what should I do?
借りた金を早く返すよう警告した。
I advised him that he should pay back the money he borrowed soon.
あの選手はどの試合でも必ず警告のイエローカードを出されるね。
That player gets a yellow card warning in every game.