The Collaborative International Dictionary of English v.0.48:

Heat \Heat\ (h[=e]t), n. [OE. hete, h[ae]te, AS. h[=ae]tu,
   h[=ae]to, fr. h[=a]t hot; akin to OHG. heizi heat, Dan. hede,
   Sw. hetta. See Hot.]
   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.
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   Note: 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.
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   2. 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.
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   3. 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.
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            Else how had the world . . .
            Avoided pinching cold and scorching heat! --Milton.
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   4. 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.
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            It has raised . . . heats in their faces. --Addison.
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            The heats smiths take of their iron are a blood-red
            heat, a white-flame heat, and a sparkling or welding
            heat.                                 --Moxon.
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   5. 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.
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   6. 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.
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            Many causes . . . for refreshment betwixt the heats.
                                                  --Dryden.
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            [He] struck off at one heat the matchless tale of
            "Tam o' Shanter."                     --J. C.
                                                  Shairp.
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   7. Utmost violence; rage; vehemence; as, the heat of battle
      or party. "The heat of their division." --Shak.
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   8. Agitation of mind; inflammation or excitement;
      exasperation. "The heat and hurry of his rage." --South.
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   9. Animation, as in discourse; ardor; fervency; as, in the
      heat of argument.
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            With all the strength and heat of eloquence.
                                                  --Addison.
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   10. (Zool.) Sexual excitement in animals; readiness for
       sexual activity; estrus or rut.
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   11. Fermentation.
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   12. Strong psychological pressure, as in a police
       investigation; as, when they turned up the heat, he took
       it on the lam. [slang]
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   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[deg] Centigrade,
      or 32[deg] Fahrenheit.
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