1. 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 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.
4. 1. The condition of being hot.
   2. A degree of warmth or hotness: The burner was on low heat.
5. 1. 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.
   2. 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.
7. 1. Intensity, as of passion, emotion, color, appearance, or effect.
   2. The most intense or active stage: the heat of battle.
   3. A burning sensation in the mouth produced by spicy flavoring in food.
8. Estrus.
9. One of a series of efforts or attempts.
10. 1. Sports & Games. One round of several in a competition, such as a race.
    2. A preliminary contest held to determine finalists.
11. Informal. Pressure; stress.
12. Slang.
    1. An intensification of police activity in pursuing criminals.
    2. 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.

1. To make warm or hot.
2. To excite the feelings of; inflame.
3. To increase the molecular or kinetic energy of (an object).

1. To become warm or hot.
2. To become excited emotionally or intellectually.

heat up Informal.

1. To become acute or intense: "If inflation heats up, interest rates could increase" (Christian Science Monitor).

[Middle English hete, from Old English hǣtu.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.