heat index

noun

plural heat indexes or heat indices

: a value that indicates what the ambient temperature feels like to the human body and that is derived from a calculation using air temperature and relative humidity

The most likely chances for a heat advisory are Thursday and Friday, when the heat index could approach at least 100 degrees, according to National Weather Service meteorologists …

—Julie E. Greene

The heat index is defined as a function of temperature and relative humidity. The combination of the two results in an apparent temperature that gives an idea of what the hot and humid air feels like to the average person.

—Neil MacFarquhar

Examples of heat index in a Sentence

Recent Examples on the Web

The heat dome brought temperatures above 100 degrees in many locations and dangerous heat indices exceeding 110 degrees in some areas. — Ignacio Calderon, USA Today, 10 Sep. 2026

Combined with a brutal noon start time that provided no shade or relief throughout the game, the conditions meant there weren’t many fans brave enough, or quite frankly dumb enough, to endure a heat index of roughly 105 degrees. — Ian Miller Outkick, FOXNews.com, 9 Sep. 2026

Temperatures are expected to jump back into the mid-90s to around 100 degrees, with heat index values near 105 degrees, the weather service said. — Kansas City Star, 8 Sep. 2026

Eachus studied the air temperature, heat indexes and peak temperatures for games at Texas, Tulsa, Alabama, Georgia, Nebraska and Iowa. — Christopher Kamrani, New York Times, 7 Sep. 2026

Word History

First Known Use

1984, in the meaning defined above