HEAT, n. [L. aestus, for haestus, or caestus.]

1. Heat, as a cause of sensation, that is, the matter of heat, is considered to be a subtil fluid, contained in a greater or less degree in all bodies. In modern chimistry it is called caloric. It expands all bodies in different proportions, and is the cause of fluidity and evaporation. A certain degree of it is also essential to animal and vegetable life. Heat is latent, when so combined with other matter as not to be perceptible. It is sensible, when it is evolved and perceptible. Lavoisier. Encyc.
2. Heat, as a sensation, is the effect produced on the sentient organs of animals, by the passage of caloric, disengaged from surrounding bodies, to the organs. When we touch or approach a hot body, the caloric or heat passes from that body to our organs of feeling, and gives the sensation of heat. On the contrary, when we touch a cold body, the caloric passes from the hand to that body, and causes a sensation of cold. Lavoisier. Note. This theory of heat seems not to be fully settled.
3. Hot air; hot weather; as, the heat of the tropical climates.
4. Any accumulation or concentration of the matter of heat or caloric; as, the heat of the body; the heat of a furnace; a red heat; a white heat; a welding heat.
5. The state of being once heated or hot. Give the iron another heat.
6. A violent action unintermitted; a single effort. Many causes are required for refreshment between the heats. Dryden.
7. A single effort in running; a course at a race. Hector won at the first heat.
8. Redness of the face; flush. Addison.
9. Animal excitement; violent action or agitation of the system. The body is all in a heat.
10. Utmost violence; rage; vehemence; as, the heat of battle.
11. Violence; ardor; as, the heat of party.
12. Agitation of mind; inflammation or excitement; exasperation; as, the heat of passion.
13. Ardor; fervency; animation in thought or discourse. With all the strength and heat of eloquence. Addison.
14. Fermentation.

1. To grow warm or hot by fermentation, or extrication of latent heat. Green hay heats in a mow, and green corn in a bin.
2. To grow warm or hot. The iron or the water heats slowly.

1. To make hot; to communicate heat to, or cause to be hot; as, to heat an oven or a furnace; to heat iron.
2. To make feverish; as, to heat the blood.
3. To warm with passion or desire; to excite; to rouse into action. A noble emulation heats your breast. Dryden.
4. To agitate the blood and spirits with action; to excite animal action. Dryden.

1. A force in nature which is recognized in various effects, but especially in the phenomena of fusion and evaporation, and which, as manifested in fire, the sun's rays, mechanical action, chemical combination, etc., becomes directly known to us through the sense of feeling. In its nature heat is a mode of motion, being in general a form of molecular disturbance or vibration. It was formerly supposed to be a subtile, imponderable fluid, to which was given the name caloric.
   
   

   * As affecting the human body, heat produces different sensations, which are called by different names, as heat or sensible heat, warmth, cold, etc., according to its degree or amount relatively to the normal temperature of the body.

2. To make hot; to communicate heat to, or cause to grow warm; as, to heat an oven or furnace, an iron, or the like.
   
   

   Heat me these irons hot. Shak.

3. To grow warm or hot by the action of fire or friction, etc., or the communication of heat; as, the iron or the water heats slowly.
4. Heated] as, the iron though heat red- hot.
   
   
   [Obs. or Archaic] Shak.
5. The sensation caused by the force or influence of heat when excessive, or above that which is normal to the human body; the bodily feeling experienced on exposure to fire, the sun's rays, etc.; the reverse of cold.
6. To excite or make hot by action or emotion; to make feverish.
   
   

   Pray, walk softly; do not heat your blood. Shak.

7. To grow warm or hot by fermentation, or the development of heat by chemical action; as, green hay heats in a mow, and manure in the dunghill.
8. High temperature, as distinguished from low temperature, or cold; as, the heat of summer and the cold of winter; heat of the skin or body in fever, etc.
   
   

   Else how had the world . . .
   Avoided pinching cold and scorching heat! Milton.

9. To excite ardor in; to rouse to action; to excite to excess; to inflame, as the passions.
   
   

   A noble emulation heats your breast. Dryden.

10. Indication of high temperature; appearance, condition, or color of a body, as indicating its temperature; redness; high color; flush; degree of temperature to which something is heated, as indicated by appearance, condition, or otherwise.
    
    

    It has raised . . . heats in their faces. Addison.

    The heats smiths take of their iron are a blood-red heat, a white-flame heat, and a sparkling or welding heat. Moxon.

11. A single complete operation of heating, as at a forge or in a furnace; as, to make a horseshoe in a certain number of heats.
12. A violent action unintermitted; a single effort; a single course in a race that consists of two or more courses; as, he won two heats out of three.
    
    

    Many causes . . . for refreshment betwixt the heats. Dryden.

    [He] struck off at one heat the matchless tale of "Tam o' Shanter." J. C. Shairp.

13. Utmost violence; rage; vehemence; as, the heat of battle or party.
    
    
    "The heat of their division." Shak.
14. Agitation of mind; inflammation or excitement; exasperation.
    
    
    "The heat and hurry of his rage." South.
15. Animation, as in discourse; ardor; fervency.
    
    

    With all the strength and heat of eloquence. Addison.

16. Sexual excitement in animals.
17. Fermentation.
    
    

    Animal heat, Blood heat, Capacity for heat, etc. See under Animal, Blood, etc. -- Atomic heat (Chem.), the product obtained by multiplying the atomic weight of any element by its specific heat. The atomic heat of all solid elements is nearly a constant, the mean value being 6.4. -- Dynamical theory of heat, that theory of heat which assumes it to be, not a peculiar kind of matter, but a peculiar motion of the ultimate particles of matter. Heat engine, any apparatus by which a heated substance, as a heated fluid, is made to perform work by giving motion to mechanism, as a hot-air engine, or a steam engine. -- Heat producers. (Physiol.) See under Food. -- Heat rays, a term formerly applied to the rays near the red end of the spectrum, whether within or beyond the visible spectrum. -- Heat weight (Mech.), the product of any quantity of heat by the mechanical equivalent of heat divided by the absolute temperature; -- called also thermodynamic function, and entropy. -- Mechanical equivalent of heat. See under Equivalent. -- Specific heat of a substance (at any temperature), the number of units of heat required to raise the temperature of a unit mass of the substance at that temperature one degree. -- Unit of heat, the quantity of heat required to raise, by one degree, the temperature of a unit mass of water, initially at a certain standard temperature. The temperature usually employed is that of 0° Centigrade, or 32° Fahrenheit.