The form of the indefinite article used before words beginning with a vowel sound.See a
Is it ’ a historical document’ or ’ an historical document’? ‘ A hotel’ or ‘ an hotel’? There is still some divergence of opinion over which form of the indefinite article should be used before words that begin with h- and have an unstressed first syllable. In the 18th and 19th centuries people often did not pronounce the initial h for these words, and so an was commonly used. Today the h is pronounced, and so it is logical to use a rather than an. However, the indefinite article an is still encountered before the h in both British and American English, particularly with historical: in the Oxford English Corpus around a quarter of examples of historical are preceded with an rather than a
Andaman and Nicobar Islands.