AN, adjective [Latin 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.' Exodus 6:8. 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.; Latin an if or whether. It is probably an imperative, like if, gif, give.