a measurement of how hot the air feels and how uncomfortable people are likely to be based on the temperature combined with the humidity (= the amount of water in the air)

With the sun beating down and a heat index of 105 degrees I was a sweaty, panting mess by the time I arrived. 骄阳似火，炎热指数高达105，我到达的时候已是汗流浃背，气喘吁吁。

a measurement of how hot (= spicy-tasting) a food such as a chilli is

If you’re brave enough to use this pepper which has a heat index of 200,000-300,000 Scoville units, it is great for salsa and marinades. 如果你敢于用这种辣指数为20万-30万斯科维尔单位的辣椒，其实它们非常适合用来制作沙拉酱和腌制酱。