'H' definitions:

Definition of 'H'

From: WordNet
noun
A nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe [syn: hydrogen, H, atomic number 1]
noun
A unit of inductance in which an induced electromotive force of one volt is produced when the current is varied at the rate of one ampere per second [syn: henry, H]
noun
The constant of proportionality relating the energy of a photon to its frequency; approximately 6.626 x 10^-34 joule- second [syn: Planck's constant, h]
noun
The 8th letter of the Roman alphabet [syn: H, h]
noun
(thermodynamics) a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure; "enthalpy is the amount of energy in a system capable of doing mechanical work" [syn: heat content, total heat, enthalpy, H]

Definition of 'H'

From: GCIDE
  • Ion \I"on\ ([imac]"[o^]n), n. [Gr. 'io`n, neut, of 'iw`n, p. pr. of 'ie`nai to go.]
  • 1. (Elec. Chem.) an atom or goup of atoms (radical) carrying an electrical charge. It is contrasted with neutral atoms or molecules, and free radicals. Certain compounds, such as sodium chloride, are composed of complementary ions in the solid (crystalline) as well as in solution. Others, notably acids such as hydrogen chloride, may occur as neutral molecules in the pure liquid or gas forms, and ionize almost completely in dilute aqueous solutions. In solutions (as in water) ions are frequently bound non-covalently with the molecules of solvent, and in that case are said to be solvated. According to the electrolytic dissociation theory, the molecules of electrolytes are divided into ions by water and other solvents. An ion consists of one or more atoms and carries one unit charges of electricity, 3.4 x 10^-10 electrostatic units, or a multiple of this. Those which are positively electrified (hydrogen and the metals) are called cations; negative ions (hydroxyl and acidic atoms or groups) are called anions.
  • Note: Thus, hydrochloric acid (HCl) dissociates, in aqueous solution, into the hydrogen ion, H+, and the chlorine ion, Cl-; ferric nitrate, Fe(NO3)3, yields the ferric ion, Fe+++, and nitrate ions, NO3-, NO3-, NO3-. When a solution containing ions is made part of an electric circuit, the cations move toward the cathode, the anions toward the anode. This movement is called migration, and the velocity of it differs for different kinds of ions. If the electromotive force is sufficient, electrolysis ensues: cations give up their charge at the cathode and separate in metallic form or decompose water, forming hydrogen and alkali; similarly, at the anode the element of the anion separates, or the metal of the anode is dissolved, or decomposition occurs. Aluminum and chlorine are elements prepared predominantly by such electrolysis, and depends on dissolving compounds in a solvent where the element forms ions. Electrolysis is also used in refining other metals, such as copper and silver. Cf. Anion, Cation. [Webster 1913 Suppl.]
  • 2. One of the small electrified particles into which the molecules of a gas are broken up under the action of the electric current, of ultraviolet and certain other rays, and of high temperatures. To the properties and behavior of ions the phenomena of the electric discharge through rarefied gases and many other important effects are ascribed. At low pressures the negative ions appear to be electrons; the positive ions, atoms minus an electron. At ordinary pressures each ion seems to include also a number of attached molecules. Ions may be formed in a gas in various ways. [Webster 1913 Suppl.]

Definition of 'H'

From: GCIDE
  • H \H\ ([=a]ch), the eighth letter of the English alphabet, is classed among the consonants, and is formed with the mouth organs in the same position as that of the succeeding vowel. It is used with certain consonants to form digraphs representing sounds which are not found in the alphabet, as sh, th, [th], as in shall, thing, [th]ine (for zh see [sect]274); also, to modify the sounds of some other letters, as when placed after c and p, with the former of which it represents a compound sound like that of tsh, as in charm (written also tch as in catch), with the latter, the sound of f, as in phase, phantom. In some words, mostly derived or introduced from foreign languages, h following c and g indicates that those consonants have the hard sound before e, i, and y, as in chemistry, chiromancy, chyle, Ghent, Ghibelline, etc.; in some others, ch has the sound of sh, as in chicane. See Guide to Pronunciation, [sect][sect] 153, 179, 181-3, 237-8. [1913 Webster]
  • Note: The name (aitch) is from the French ache; its form is from the Latin, and this from the Greek H, which was used as the sign of the spiritus asper (rough breathing) before it came to represent the long vowel, Gr. [eta]. The Greek H is from Ph[oe]nician, the ultimate origin probably being Egyptian. Etymologically H is most closely related to c; as in E. horn, L. cornu, Gr. ke`ras; E. hele, v. t., conceal; E. hide, L. cutis, Gr. ky`tos; E. hundred, L. centum, Gr. "e-kat-on, Skr. [.c]ata. [1913 Webster]
  • H piece (Mining), the part of a plunger pump which contains the valve. [1913 Webster]

Definition of 'H'

From: GCIDE
  • H \H\ (h[aum]). (Mus.) The seventh degree in the diatonic scale, being used by the Germans for B natural. See B. [1913 Webster]

Words containing 'H'