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1. Physics
a. A form of energy associated with the kinetic energy of atoms or molecules and capable of being transmitted through solid and fluid media by conduction, through fluid media by convection, and through empty space by radiation.
b. The transfer of energy from one body to another as a result of a difference in temperature or a change in phase.
2. The sensation or perception of such energy as warmth or hotness.
3. An abnormally high bodily temperature, as from a fever.
a. The condition of being hot.
b. A degree of warmth or hotness: The burner was on low heat.
a. The warming of a room or building by a furnace or another source of energy: The house was cheap to rent, but the heat was expensive.
b. A furnace or other source of warmth in a room or building: The heat was on when we returned from work.
6. A hot season; a spell of hot weather.
a. Intensity, as of passion, emotion, color, appearance, or effect.
b. The most intense or active stage: the heat of battle.
c. A burning sensation in the mouth produced by spicy flavoring in food.
8. Estrus.
9. One of a series of efforts or attempts.
a. Sports & Games One round of several in a competition, such as a race.
b. A preliminary contest held to determine finalists.
11. Informal Pressure; stress.
12. Slang
a. An intensification of police activity in pursuing criminals.
b. The police. Used with the.
13. Slang Adverse comments or hostile criticism: Heat from the press forced the senator to resign.
14. Slang A firearm, especially a pistol.
v. heat·ed, heat·ing, heats
1. To make warm or hot.
2. To excite the feelings of; inflame.
3. Physics To increase the heat energy of (an object).
1. To become warm or hot.
2. To become excited emotionally or intellectually.
Phrasal Verb:
heat up Informal
To become acute or intense: "If inflation heats up, interest rates could increase" (Christian Science Monitor).

[Middle English hete, from Old English hǣtu; see kai- in Indo-European roots.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


Preliminary races to eliminate slower runners in crowded events.
Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited
References in classic literature ?
The thin covering of earth on the rock supported but a scanty and faded herbage, and most of the trees that had found root in the fissures had already died, during the in tense heats of preceding summers.
After this, I spent a great deal of time and pains to make an umbrella; I was, indeed, in great want of one, and had a great mind to make one; I had seen them made in the Brazils, where they are very useful in the great heats there, and I felt the heats every jot as great here, and greater too, being nearer the equinox; besides, as I was obliged to be much abroad, it was a most useful thing to me, as well for the rains as the heats.
"It is known now that heat is only a modification of motion.
Chief Inspector Heat of the Special Crimes Department changed his tone.
"You will now readily understand, gentlemen, the apparatus that I have described to you is really a gas cylinder and blow-pipe for oxygen and hydrogen, the heat of which exceeds that of a forge fire.
Heating is the contrary of cooling, being heated of being cooled, being glad of being vexed.
JULY CAME ON with that breathless, brilliant heat which makes the plains of Kansas and Nebraska the best corn country in the world.
Besides, I wish such persons to observe that the grand artery and the arterial vein are of much harder and firmer texture than the venous artery and the hollow vein; and that the two last expand before entering the heart, and there form, as it were, two pouches denominated the auricles of the heart, which are composed of a substance similar to that of the heart itself; and that there is always more warmth in the heart than in any other part of the body- and finally, that this heat is capable of causing any drop of blood that passes into the cavities rapidly to expand and dilate, just as all liquors do when allowed to fall drop by drop into a highly heated vessel.
Volcanoes, so plentiful in the first days of the world, are being extinguished by degrees; the internal heat is weakened, the temperature of the lower strata of the globe is lowered by a perceptible quantity every century to the detriment of our globe, for its heat is its life."
An almost noise- less and blinding flash of light, and a man fell headlong and lay still; and as the unseen shaft of heat passed over them, pine trees burst into fire, and every dry furze bush became with one dull thud a mass of flames.
The house was big and old-fashioned, and Levin, though he lived alone, had the whole house heated and used.
The snatches of conversation which he had caught between Christine and the monster had contributed not a little to drive him beside himself: add to that the shock of the magic forest and the scorching heat which was beginning to make the prespiration{sic} stream down his temples and you will have no difficulty in understanding his state of mind.