Note: ☞ An is used before a word beginning with a vowel sound; as, an enemy, an hour. It in also often used before h sounded, when the accent of the word falls on the second syllable; as, an historian, an hyena, an heroic deed. Many writers use a before h in such positions. Anciently an was used before consonants as well as vowels.
Etymology: AS. ān one, the same word as the numeral. See One, and cf. A