The words risky and dangerous can be used in similar contexts, but risky often applies to a known and accepted danger.

// shied away from risky investments

The meanings of hazardous and dangerous largely overlap; however, hazardous implies great and continuous risk of harm or failure.

// claims that smoking is hazardous to your health

Some common synonyms of dangerous are hazardous, perilous, precarious, and risky. While all these words mean "bringing or involving the chance of loss or injury," dangerous applies to something that may cause harm or loss unless dealt with carefully.

// soldiers on a dangerous mission