thermal
n. countablen. a rising current of warm air that birds or gliders use to stay high in the sky. You can also use this word to talk about a piece of clothing that keeps you warm.
n. a rising column of warm air caused by the uneven heating of the Earth's surface. In a military or technical context, it may also refer to an image produced by infrared radiation or a garment designed for heat retention.
The eagle circled higher by catching a thermal.
The glider pilot searched for a strong thermal to gain enough altitude to cross the mountain range.
Modern reconnaissance drones utilize high-resolution thermal imaging to detect heat signatures from vehicles and personnel through dense foliage or total darkness.
From French thermal, from New Latin thermalis, from Ancient Greek θέρμη (thérmē, “heat”), from Proto-Indo-European gʷʰer- (“to heat, warm”).
Often used in the plural when referring to warm undergarments ('wearing thermals').