i

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

• noun The ninth letter of the modern English alphabet.
• noun Any of the speech sounds represented by the letter i.
• noun The ninth in a series.
• noun Something shaped like the letter I.

from The Century Dictionary.

• The ninth letter and third vowel in the English alphabet.
• The Phenician character represented rather a consonant, a y, than a vowel, but it was converted to vowel value by the Greeks, and has continued to bear that value since (though in Latin used as consonant also). Our “short i” of it, etc., is not far from the original sound; yet nearer is the sound which we perversely call “long e” (of mete, meet, meat, etc.), or the i of machine, pique, etc. Because the words which anciently showed this latter sound have in great measure changed it to a diphthongal utterance (nearly ä + i, or the ai of aisle), we have come to call the altered sound “long i.” The true i-sounds (in pick, pique) are close vowels, made with as near an approximation of the organs as is possible without giving rise to a fricative utterance. The approximation is made by the upper flat surface of the tongue to the palate, at or near the point where a complete closure makes a k-sound. Hence the i-sound has palatal affinities, and it (as also in less degree the e) is widely active in palatalizing a consonant: for example, in converting in modern English a t to ch, a d to j, an s to sh, a z to zh; having in older English, and in other languages, a like influence on a k or g. Hence, also, it is a vowel close to a consonant, and very nearly identical with the consonantal y, into which it passes freely. (See Y.) I has also gained in many words before r the same sound that e and u have in the same situation: for example, fir, first. It enters into various digraphs, as ai, ei, ie, oi, ui.
• As a symbol: The number one in the Roman notation.
• In logic, a symbol of the particular affirmative proposition: derived from the second vowel of the Latin word affirmo, I assert. See A, 2 .
• In chem., the symbol for iodine.
• An abbreviation
• In dental formulæ, in zoology, for incisor.
• Same as i. e.
• See i. e., i. q.
• noun A prefix (often spelled y-, and sometimes e- and a-) common in Middle English, as in i-blent, i-cast, i-don, i-take, i-cleped, i-wis, etc. (also spelled y-blent, y-cast, y-don, etc.), but entirely lost in modern English, except as traces remain in y-wis, adv. (sometimes erroneously written I wis), and in y-clept and a few other archaic perfect-participle forms affected by Spenser and other poets, and in alike, along, among, enough, everywhere, handiwork, and a few other common words in which the syllable concerned is not now recognized as a prefix.
• noun An apparent connective, but properly a prefix, in hand-i-work and hand-i-craft (altered from hand-craft in imitation of handiwork), and (now spelled -y-) in ever-y-where. See these words, and compare i-.
• The usual symbol for the moment of inertia.
• In electricity, a symbol for current.
• In mathematics: The symbol (i or i) for the neomon, the square root of minus one (√—1, (—1)). In quaternions, the symbols i, j, k denote a system of three right versors in three mutually rectangular planes; thus i is a particular quaternion having for its amplitude one right angle.
• In chem., i- before certain compounds has reference to their inaction as distinguished from dextro-rotation (d-) or levorotation (1-).
• An abbreviation of Idaho;
• of the Latin Imperator, emperor;
• of Island;
• of intransitive.
• noun An occasional obsolete spelling of eye.
• noun A form of the negative prefix in- before gn- in some words of Latin origin, as in ignoble, ignore, ignorant, etc.
• noun In philology an abbreviation of Indo-Euro-pean.
• The ending of some Latin genitives singular of nouns and adjectives of the second declension, occurring in some ancient, medieval or modern Latin phrases used in English, as genius loci, lapis lazuli, quid novi, etc.
• The nominative case of the pronoun of the first person; the word by which a speaker or writer denotes himself.
• noun The pronoun I used as a substantive.
• noun In metaphysics, the object of self-consciousness; that which is conscious of itself as thinking, feeling, and willing; the ego.
• An obsolete form of aye.
• noun A light form of in: as, “a worm i' the bud,’
• noun The usual ‘connecting vowel,’ properly the stem-vowel of the first element, of compound words taken or formed from the Latin, as in mult-i-form, cent-i-ped, ens-i-form, omn-i-potent, aur-i-ferous, bell-i-gerent, etc.
• A nominative plural ending of Latin masculine nouns and adjectives of the ‘second’ declension, with nominative singular in -us, or without suffix, many of which have come into English use, literary or technical.
• A nominative plural suffix of Italian nouns sometimes used in English, as banditti, dilettanti, lazzaroni, scudi, soprani, etc.

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

• pronoun The nominative case of the pronoun of the first person; the word with which a speaker or writer denotes himself.
• I, the ninth letter of the English alphabet, takes its form from the Phœnician, through the Latin and the Greek. The Phœnician letter was probably of Egyptian origin. Its original value was nearly the same as that of the Italian I, or long e as in mete. Etymologically I is most closely related to e, y, j, g; as in dint, dent, beverage, L. bibere; E. kin, AS. cynn; E. thin, AS. þynne; E. dominion, donjon, dungeon.
• In our old authors, I was often used for ay (or aye), yes, which is pronounced nearly like it.
• As a numeral, I stands for 1, II for 2, etc.

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

• noun cardinal number one.
• noun mathematics The imaginary unit that is the positive square root of -1. Graphically, i is shown on the vertical (y-axis) plane.
• noun engineering The current flow in a circuit in amperes.
• noun programming A common variable name representing a generic index, especially in loops.
• noun close front unrounded vowel.
• noun The ninth letter of the English alphabet, called i and written in the Latin script.
• noun The ordinal number ninth, derived from this letter of the English alphabet, called i and written in the Latin script.
• noun The name of the Latin script letter I/i.
• noun The ninth letter of the basic modern Latin alphabet.
• pronoun obsolete capitalization of I