h

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The eighth letter of the modern English alphabet.
• noun Any of the speech sounds represented by the letter h.
• noun The eighth in a series.
• noun Something shaped like the letter H.
• abbreviation height
• abbreviation hour

from The Century Dictionary.

• noun An abbreviation of His Holiness —that is, the Pope—or of His (or Her) Highness.
• noun An abbreviation in epitaphs of the Latin phrase hic jacet (which see).
• noun An abbreviation of House of Lords.
• An abbreviation of His (or Her) Majesty.
• An abbreviation of horse-power.
• An abbreviation of House of Representatives.
• In mineralogy, the initial letter of the general symbol, hkl, applied to a face of a crystal in the system of Miller. See symbol.
• In electricity, the symbol for henry (which see).
• In pathol., hypermetropia.
• noun An abbreviation of Heralds' College.
• noun An abbreviation of His Eminence;
• noun of Bis (or Her) Excellency;
• noun of Hydraulic Engineer.
• noun An abbreviation of the Latin hic est, ‘he is’; of the Latin hoc est, ‘this is.’
• noun An abbreviation
• noun of His Grace;
• noun of Horse Guards.
• noun An abbreviation of Hawaiian Islands.
• noun An abbreviation
• noun of Hallelujah Meter;
• noun of Home Mission or Home Missionary.
• noun An abbreviation of half pay;
• noun of High Priest;
• noun of high-pressure, when applied to cyliuders: when applied to engines it means horse-power, and, to prevent confusion, when a high-pressure engine is meant the words should be written out.
• noun An abbreviation of headquarters.
• noun An abbreviation of Home Ruler.
• noun In electricity, an abbreviation of high resistance.
• noun An abbreviation of hoc titulo, ‘in (or under) this title.’
• noun An abbreviation of House of Commons.
• The eighth letter and sixth consonant in the English alphabet.
• The sound belonging to the character in Phenician was that of a rough guttural spirant, nearly like the ch in German, or in Scotch loch (marked in this dictionary ċh). In the Greek alphabet it had at first the kindred but weaker value of our h; and with this value it passed over to Italy, and so continued there; but in Greece it came later to be used as a long ē (down to that time long and short e had been written alike E), the h-sound being indicated by a half H, namely ├, afterward reduced to └ and ‘, which last then retained the h-value, or that of the “rough breathing,” so called, now usually printed’. Our h-sound is called the “aspiration,” as being a near approach to pure unmodified breathing, an audible emission of breath before a vowel or semivowel, made, in every case, in the same position of the mouth-organs as that required by the following sound. That is, the h of ha is made in the mouth-position of a, the utterance in the combination changing only from unintonated to intonated breath; that of he is made in the mouth-position of ee;.and so with ho, and so on. Thus, the h before each different vowel represents a different product, and h signifies a sort of common surd to all the vowels as sonants; and, being dependent always for its special character upon the following sound, it is very suitably written by the Greeks with a subordinate sign prefixed to the vowel. In English the aspiration occurs before all the vowels, and also before the semivowels w and y, as in whit (that is, hwit) and hue (that is, hyu), though in these cases some authorities hold that the w- and y-sounds themselves are not uttered, but only the h-sound, this being what it would be if the semivowel were really pronounced. This view may in part depend upon an actual difference of pronunciation, but is more probably an error of apprehension and analysis; certainly, in our ordinary utterance, whit is to hoo-it precisely as wit is to oo-it. In older English our h-sound was pronounced also before r and l, as in AS. hring, English ring, AS. hrīm, English rime, AS. hrōf, English roof, AS. hlāf, English loaf, AS. hlid, English lid, AS. hliehhan, English laugh, etc.; in other languages it is found also before m and n. The English h in the Teutonic part of the language comes from an original surd guttural, a k, which first became a guttural spirant (= ch in German, or in Scotch loch), and was then further weakened to a mere aspiration. The spirant becomes mere aspiration when its production ceases to be accompanied with a constriction at the top of the throat, causing a rough fricative sound, and so giving a specific character to the utterance. A guttural mute was changed to a spirant also in the interior of many of our words, and was formerly written with h: thus, AS. niht, English night; but it has long been lost in pronunciation, after being written with gh instead of h (the g never pronounced). The aspiration, indeed, being the weakest and least positive of alphabetic sounds, is especially liable to become silent. The Latin initial h was totally silent in the vernacular forms which emerged as Old French and Italian, and in the earliest Old French, as still in Italian, it does not appear in writing. The earliest Old French words, therefore, having original Latin h, were transferred into Middle English without h, as abit, able, eir, onest, onor, onur, oure, ure, etc., through similar Old French forms from Latin habitus, habilis, heres, honestus, honor, hora, etc. In later Old French and Middle English the pedantic habit of imitating the spelling of the original Latin, if known, led to the general restoration of h in these words, a restoration completed in modern French, though the h has remained always unpronounced in French, and, in the oldest and most familiar words, in English. The h now appears in the modern forms of all the above words, and others (except able and arbor, the restored forms hable, harbor, having died out), namely, unpronounced in heir, honest, honor, hour, etc., and pronounced (by conformity to later words) in habit, heretic, etc., while in some, as herb, humble, etc., the pronunciation wavers between the earlier unaspirated form and the later aspirated form. The confusion existing in such cases led to some variation in the spelling of words originally and properly beginning with a vowel, the h, though not pronounced, being often erroneously inserted in writing, as in habandon, habound, habundance, etc., for abandon, abound, abundance, etc. A similar confusion extended to words of Anglo-Saxon or other Teutonic origin, the h being dropped sometimes where it should appear, and, more often, inserted where it should not appear, as hape for ape, his for is, etc. This confusion characterizes the present pronunciation of the London cockney. The habitual omission of h is, however, quite common even in educated speech in certain positions, and even where usually uttered it is apt to be lost after a final consonant in rapid and easy speaking. In the pronouns he, him, her, when unaccented, as they usually are after another word, the h is almost universally omitted in colloquial speech, an omission long recognized in the common spelling of the related neuter pronoun hit, now always written and pronounced it, and in the colloquial plural hem, now written 'em. The h forms a number of digraphs, or compound characters, some of them of great importance and frequency. The origin of this practice goes back to the earliest Greek period, when the so-called aspirates were real aspirates— that is, mutes with an audible bit of flatus expelled after them: kh nearly as in backhouse, th as in boat-hook, ph as in haphazard. The sounds were at first so written in Greek, with an h after each mute; later, simple characters were devised to take the place of these combinations. But in Greek words carried into Italy the spelling with h was kept up: thus, chorus, theatrum, philosophus; then, in the change of these aspirates to spirants, unitary values were won by the digraphs; and the use of th, especially with spirant value (thin, that), was widely extended to the Teutonic part of our language. The digraph sh comes by alteration of the k of sk to a spirant, and its fusion with the sibilant, making a more palatal sibilant. The origin of our gh (always either silent or pronounced as f), by graphic change from earlier h, has been stated above. (See also under G.) Finally, rh is found in Greek words, as rhetoric, and represents an r with preceding aspiration, as in AS. hring (whence it should properly be written hr, as hw for wh); but the aspiration is always lost in our utterance. For the name of the letter, see aitch.
• As a medieval numeral, 200. and with a dash over it, thus, , 200,000.
• As a symbol:
• As an abbreviation: , , ,

from the GNU version of the Collaborative International Dictionary of English.

• 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, �, as in shall, thing, �ine (for zh see §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, §§ 153, 179, 181-3, 237-8.
• (Mining) the part of a plunger pump which contains the valve.
• (Mus.) The seventh degree in the diatonic scale, being used by the Germans for B natural. See b.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The eighth letter of the English alphabet, called aitch and written in the Latin script.
• noun The ordinal number eighth, derived from this letter of the English alphabet, called aitch and written in the Latin script.
• noun The eighth letter of the basic modern Latin alphabet.
• noun voiceless glottal fricative.
• noun Planck's constant
• initialism sciences abbreviation for hour (particularly when used as a (non-SI) unit of time alongside International System of Units (SI) units)