From Latin *calor*, meaning "heat" or "warmth," from the verb *calēre* ("to be warm"). The same Latin root gives English "calorie" and "caloric," and Spanish cognates like *calentar* (to heat) and *cálido* (warm/hot).

In Spain and Latin America, *calor* is a constant topic of daily conversation, especially in summer. The phrase *hacer calor* ("to make heat") is the standard way to say the weather is hot — Spanish says the weather *makes* heat rather than *being* hot, so never say *"está calor"*; always say *"hace calor"*. Also note that *calor* is grammatically masculine (*el calor*), even though many nouns ending in *-or* can vary — a common mistake is to say *"la calor,"* which is heard in some regional dialects but considered non-standard.