An
King James Dictionary [1]
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." Exodus 6 . 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 definite 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, in old English authors, signifies if as, "an it please your honor." Gr. L. an, if or whether. It is probably an imperative, like if, gif, give.
Webster's Dictionary [2]
(1): This word is properly an adjective, but is commonly called the indefinite article. It is used before nouns of the singular number only, and signifies one, or any, but somewhat less emphatically. In such expressions as "twice an hour," "once an age," a shilling an ounce (see 2d A, 2), it has a distributive force, and is equivalent to each, every.
(2): (conj.) If; - a word used by old English authors.
