1. the state of a body perceived as having or generating a relatively high degree of warmth.
  2. the condition or quality of being hot: the heat of an oven.
  3. the degree of hotness; temperature: moderate heat.
  4. the sensation of warmth or hotness: unpleasant heat.
  5. a bodily temperature higher than normal: the heat of a fever; the feeling of heat caused by physical exertion.
  6. added or external energy that causes a rise in temperature, expansion, evaporation, or other physical change.
  7. Physics. a nonmechanical energy transfer with reference to a temperature difference between a system and its surroundings or between two parts of the same system. Symbol: Q
  8. a hot condition of the atmosphere or physical environment; hot season or weather.
  9. a period of hot weather.
  10. a sharp, pungent flavor, as that produced by strong spices.
  11. warmth or intensity of feeling; vehemence; passion: He spoke with much heat and at great length.
  12. maximum intensity in an activity, condition, etc.; the height of any action, situation, or the like: the heat of battle; the heat of passion.
  13. extreme pressure, as of events, resulting in tension or strain: In the heat of his hasty departure he forgot his keys.
  14. a single intense effort; a sustained, concentrated, and continuous operation: The painting was finished at a heat.
  15. Slang. intensified pressure, especially in a police investigation.
  16. Slang. the police.
  17. Slang. armed protection, especially a pistol, revolver, or other firearm: All guards carry some heat.
  18. Sports.
    1. a single course in or division of a race or other contest.
    2. a race or other contest in which competitors attempt to qualify for entry in the final race or contest.
  19. Metallurgy.
    1. a single operation of heating, as of metal in a furnace, in the treating and melting of metals.
    2. a quantity of metal produced by such an operation.
  20. Zoology.
    1. sexual receptiveness in animals, especially females.
    2. the period or duration of such receptiveness: to be in heat.

verb (used with object)

  1. to make hot or warm (often followed by up).
  2. to excite emotionally; inflame or rouse with passion.

verb (used without object)

  1. to become hot or warm (often followed by up).
  2. to become excited emotionally.

Verb Phrases

  1. heat up, to increase or become more active or intense: Business competition will heat up toward the end of the year.


    1. the energy transferred as a result of a difference in temperature
    2. the random kinetic energy of the atoms, molecules, or ions in a substance or body

    Related adjectives: thermal, calorific

  1. the sensation caused in the body by heat energy; warmth
  2. the state or quality of being hot
  3. hot weatherthe heat of summer
  4. intensity of feeling; passionthe heat of rage
  5. pressurethe political heat on the government over the economy
  6. the most intense or active partthe heat of the battle
  7. a period or condition of sexual excitement in female mammals that occurs at oestrus
  8. sport
    1. a preliminary eliminating contest in a competition
    2. a single section of a contest
  9. slang police activity after a crimethe heat is off
  10. mainly US slang criticism or abusehe took a lot of heat for that mistake
  11. in the heat of the moment without pausing to think
  12. on heat or in heat
    1. Also: in season(of some female mammals) sexually receptive
    2. in a state of sexual excitement
  13. the heat slang the police
  14. turn up the heat or turn on the heat informal to increase the intensity of activity, coercion, etc


  1. to make or become hot or warm
  2. to make or become excited or intense

Old English hætu, hæto “heat, warmth; fervor ardor,” from Proto-Germanic *haiti- “heat” (cf. Old Saxon hittia, Old Norse hiti, Old Frisian hete, German hitze “heat,” Gothic heito “fever”), from PIE *kaid-, from root *kai- “heat.” The same root is the source of Old English hat “hot” and hæða “hot weather” (see hot).

Meaning “a single course in a race,” especially a horse race, is from 1660s, perhaps from earlier figurative sense of “violent action; a single intense effort” (late 14c.), or meaning “run given to a horse to prepare for a race” (1570s). This later expanded to “division of a race or contest when there are too many contestants to run at once,” the winners of each heat then competing in a final race. Meaning “sexual excitement in animals” is from 1768. Meaning “trouble with the police” attested by 1920. Heat wave “period of excessive hot weather” first attested 1890; earlier in reference to solar cycles.


Old English hætan “to heat; to become hot,” from Proto-Germanic *haitijanam (see heat (n.)). Related: Heated (with many variants in Middle English); heating. Cf. Middle Dutch heeten, Dutch heten, German heizen “to heat.”


  1. A form of energy associated with the motion 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.
  2. The sensation or perception of such energy as warmth or hotness.
  3. An abnormally high bodily temperature, as from a fever.
  4. Estrus.

  1. Internal energy that is transferred to a physical system from outside the system because of a difference in temperature and does not result in work done by the system on its surroundings. Absorption of energy by a system as heat takes the form of increased kinetic energy of its molecules, thus resulting in an increase in temperature of the system. Heat is transferred from one system to another in the direction of higher to lower temperature. See also thermodynamics. See Note at temperature.
  2. See estrus.

In physics, a form of energy associated with the movement of atoms and molecules in any material. The higher the temperature of a material, the faster the atoms are moving, and hence the greater the amount of energy present as heat. (See infrared radiation.)

In addition to the idioms beginning with heat

  • heat up

also see:

  • dead heat
  • in heat
  • in the heat of the moment
  • turn up the heat

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