KJV Dictionary Definition: an
AN, a. L. unus, una, unum; Gr.
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. 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.