heat index

[ heet in-deks ]

noun

, Meteorology.

1. a formulaically calculated approximation of how hot it feels given the temperature of the air combined with the relative humidity, based on the fact that an actual temperature will feel warmer as the relative humidity rises and causes a decrease in the natural evaporative cooling from perspiration. : HI, H.I.

heat index

1. A measurement of the air temperature in relation to the relative humidity, used as an indicator of discomfort. The heat index is higher when high air temperatures occur with high humidity, and lower when they occur with low humidity. The heat index is based on studies of skin cooling caused by the evaporation of sweat.
2. Also called apparent temperature

Word History and Origins

Origin of heat index¹

First recorded in 1975–80

Example Sentences

Humidity remains high, so a heat index around 100 is possible at times during peak heating.

From Washington Post

High heat indexes are often the reason esteemed athletes have to change their plans, says Schimelpfenig.

From Outside Online

Highs are mainly in the mid-90s, with heat index values around 100.

From Washington Post

Humidity was down a little today, just enough for heat indexes to struggle to hit 100.

From Washington Post

Dew points rise into the low 70s meaning high humidity and heat index values up to the upper 90s to about 100.

From Washington Post

Large sweat stains were visible on his shirt and jacket as the heat index approached 95 degrees.

From The Daily Beast

The tourmaline has a light-refractive index of 1.63, with a heat index of none, being to heat-rays completely opaque.

From Project Gutenberg