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

But they dropped off the pace in the second, clocking 55.04secs - the 12th-quickest time in heat two - to lose four places in the standings before Sunday's medal-deciding heats.

From BBC • Feb. 21, 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

This same process occurs in heat pumps designed to supply single homes, it just happens on a much larger scale in giant heat pumps that serve entire city districts.

From BBC • Dec. 15, 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