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

Article continues below this ad By Wednesday afternoon, temperatures are expected to reach 93 to 95 degrees under partly cloudy skies, but heat index values could peak as high as 104 degrees. — Newsroom Meteorologist, San Antonio Express-News, 30 Sep. 2026

Charlotte has experienced continual days this summer with dangerous heat indexes above 100. — Joe Marusak, Charlotte Observer, 19 Sep. 2026

The forecast for Thursday included a high temperature near 96, with heat index values as high as 102, and, into the evening, of a low of 74. — Ruby Grisin, Louisville Courier Journal, 18 Sep. 2026

Highs remain near 100°, with heat index values around 105° possible. — Michael Autovino, CBS News, 15 Sep. 2026

Word History

First Known Use

1984, in the meaning defined above