Emily Dickinson Lexicon

AN, a. [Sax. an, ane, one; D. een; Ger. ein; Sw. and Dan. en; Fr. on, un, une; Sp. un, uno; It. uno, una; L. unus, una, unum; Gr. εν; Ir. ein, ean, aon; W. un, yn; Corn. uynyn; Arm. yunan.]

One; noting an individual, either definitely, known, certain, specified, or understood; or indefinitely, not certain, known, or specified. Definitely, as “Noah built an ark of Gopher wood:” “Paul was an eminent apostle.” Indefinitely, as “Bring me an orange.” Before a consonant the letter n is dropped, as a man; but our ancestors wrote an man, an king. This letter represents an definitely, or indefinitely. Definitely, as “I will take you to me for a people, and I will be to you a God.” Ex. vi. Indefinitely, as “The province of a judge is to decide controversies.” An being the same word as one, should not be used with it; “such an one,” is tautology the true phrase is such one. Although an, a and one, are the same word, and always have the same sense, yet by custom, an and a are used exclusively as a definitive adjective, and one is used in numbering. Where our ancestors wrote an, twa, thry, we now use one, two, three. So an and a are never used except with a noun; but one, like other adjectives, is sometimes used without its noun, and as a substitute for it: “One is at a loss to assign a reason for such conduct.” An is to be used before a vowel and before a silent h, as an hour. It is also used before h when the accent of the word falls on any syllable except the first, as in historian, and historiographer.