1. [n]  a unit of length used for distances within the solar system; equal to the mean distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometers)
2. [n]  a soft yellow malleable ductile (trivalent and univalent) metallic element; occurs mainly as nuggets in rocks and alluvial deposits; does not react with most chemicals but is attacked by chlorine and aqua regia

AU is a 2 letter word that starts with A.

1. The two character country code for Australia used in internet domain names.

2. audio.