U·nit n.
 1. A single thing or person.
 2. Arith. The least whole number; one.
    Units are the integral parts of any large number.   --I. Watts.
 3. A gold coin of the reign of James I., of the value of twenty shillings.
 4. Any determinate amount or quantity (as of length, time, heat, value) adopted as a standard of measurement for other amounts or quantities of the same kind.
 5. Math. A single thing, as a magnitude or number, regarded as an undivided whole.
 Abstract unit, the unit of numeration; one taken in the abstract; the number represented by 1. The term is used in distinction from concrete, or determinate, unit, that is, a unit in which the kind of thing is expressed; a unit of measure or value; as 1 foot, 1 dollar, 1 pound, and the like.
 Complex unit Theory of Numbers, an imaginary number of the form a + b√(-1), when a² + b² = 1.
 Duodecimal unit, a unit in the scale of numbers increasing or decreasing by twelves.
 Fractional unit, the unit of a fraction; the reciprocal of the denominator; thus, ¼ is the unit of the fraction ¾.
 Integral unit, the unit of integral numbers, or 1.
 Physical unit, a value or magnitude conventionally adopted as a unit or standard in physical measurements. The various physical units are usually based on given units of length, mass, and time, and on the density or other properties of some substance, for example, water. See Dyne, Erg, Farad, Ohm, Poundal, etc.
 Unit deme Biol., a unit of the inferior order or orders of individuality.
 Unit jar Elec., a small, insulated Leyden jar, placed between the electrical machine and a larger jar or battery, so as to announce, by its repeated discharges, the amount of electricity passed into the larger jar.
 Unit of heat Physics, a determinate quantity of heat adopted as a unit of measure; a thermal unit (see under Thermal). Water is the substance generally employed, the unit being one gram or one pound, and the temperature interval one degree of the Centigrade or Fahrenheit scale. When referred to the gram, it is called the gram degree. The British unit of heat, or thermal unit, used by engineers in England and in the United States, is the quantity of heat necessary to raise one pound of pure water at and near its temperature of greatest density (39.1° Fahr.) through one degree of the Fahrenheit scale. --Rankine.
 Unit of illumination, the light of a sperm candle burning 120 grains per hour. Standard gas, burning at the rate of five cubic feet per hour, must have an illuminating power equal to that of fourteen such candles.
 Unit of measure (as of length, surface, volume, dry measure, liquid measure, money, weight, time, and the like), in general, a determinate quantity or magnitude of the kind designated, taken as a standard of comparison for others of the same kind, in assigning to them numerical values, as 1 foot, 1 yard, 1 mile, 1 square foot, 1 square yard, 1 cubic foot, 1 peck, 1 bushel, 1 gallon, 1 cent, 1 ounce, 1 pound, 1 hour, and the like; more specifically, the fundamental unit adopted in any system of weights, measures, or money, by which its several denominations are regulated, and which is itself defined by comparison with some known magnitude, either natural or empirical, as, in the United States, the dollar for money, the pound avoirdupois for weight, the yard for length, the gallon of 8.3389 pounds avoirdupois of water at 39.8° Fahr. (about 231 cubic inches) for liquid measure, etc.; in Great Britain, the pound sterling, the pound troy, the yard, or part of the length of a second's pendulum at London, the gallon of 277.274 cubic inches, etc.; in the metric system, the meter, the liter, the gram, etc.
 Unit of power. Mach. See Horse power.
 Unit of resistance. Elec. See Resistance, n., 4, and Ohm.
 Unit of work Physics, the amount of work done by a unit force acting through a unit distance, or the amount required to lift a unit weight through a unit distance against gravitation. See Erg, Foot Pound, Kilogrammeter.
 Unit stress Mech. Physics, stress per unit of area; intensity of stress. It is expressed in ounces, pounds, tons, etc., per square inch, square foot, or square yard, etc., or in atmospheres, or inches of mercury or water, or the like.
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From: Webster's Revised Unabridged Dictionary (1913)

 Heat n.
 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.
 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.
 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.
 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.
 Else how had the world . . .
 Avoided pinching cold and scorching heat!   --Milton.
 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.
    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.
 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.
 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.
    Many causes . . . for refreshment betwixt the heats.   --Dryden.
    [He] struck off at one heat the matchless tale of =\“Tam o' Shanter.”\=   --J. C. Shairp.
 7. Utmost violence; rage; vehemence; as, the heat of battle or party. “The heat of their division.”
 8. Agitation of mind; inflammation or excitement; exasperation. “The heat and hurry of his rage.”
 9. Animation, as in discourse; ardor; fervency; as, in the heat of argument.
    With all the strength and heat of eloquence.   --Addison.
 10. Zool. Sexual excitement in animals; readiness for sexual activity; estrus or rut.
 11. 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.