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
Cite this Entry
“Heat index.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/heat%20index. Accessed 8 Jul. 2026.
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