Dangerous, Risky
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of dangerous? It's dangerous.
あぶない
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: Someone is in danger! It's poor old abe (あぶ) Lincoln. You try to save him, yelling out 危ないよ！！！！, but he gets shot in the back of the head anyways.
危ない！気をつけて。
Be careful! Watch out!
スピードを出しすぎると危ないですよ。
Driving too fast is dangerous, you know.
夜道を一人で歩くのは危ないです。
Walking alone on the streets at night is dangerous.