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]

---

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

Their times in heat three and four were the sixth and 10th quickest respectively, and a shake of the head from Hall after run three illustrated his disgruntlement at how these Games have gone.

From BBC • Feb. 22, 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

An extra layer of low-moisture cheese between dough and sauce helps lock in heat for travel.

From The Wall Street Journal • Oct. 8, 2025

I, meanwhile, croaked out a laugh that sounded like a rhinoceros in heat.

From "From Twinkle, with Love" by Sandhya Menon