in heat

Idioms  

1. In a state of sexual excitement immediately preceding ovulation. For example, Our cat's in heat so we have to keep her inside. This expression applies to most female mammals and indicates the period when the animal is fertile and most receptive to mating. [Mid-1700s]

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Example Sentences

Unlike internal combustion engines, which require a large temperature gap to operate efficiently, Stirling engines can run on much smaller differences in heat.

From Science Daily • Feb. 27, 2026

If successful, Karman could dent the market share of Trane Technologies and Schneider Electric, the leaders in heat rejection systems.

From Los Angeles Times • Jan. 22, 2026

The Celtic powerbrokers, who have been engulfed in heat from the fans, knew what they were doing with this one.

From BBC • Nov. 2, 2025

Another growing use case is in data centers, where aluminum is used in heat sinks, cooling systems and the structures themselves.

From The Wall Street Journal • Oct. 10, 2025

As the flame grew in heat and height, Nathan added bigger and bigger pieces of wood.

From "Healer of the Water Monster" by Brian Young