Both nouns refer to something that is threatening or can cause harm or damage. Hazard refers to the source of potential damage, harm or adverse health effects under certain conditions. Examples can include, for instance, electricity, chemicals, certain working conditions (like climbing up a ladder), bully at work, stress. Risk, on the other hand, is the high or low chance that any kind of hazard will cause harm. In other words, it refers to a factor or a cause involving uncertain danger, hazard. It is also used as a term for the variability of returns from an investment or the amount that insurance company stands to lose. Hazard, besides a possible source of danger, has meanings in sports ad games, too. In sports, it refers to an obstacle, in games, it is the name of a dice game.