AU
| Noun | 1. |  Au - 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 regiaSynonyms: atomic number 79, gold |
| 2. | AU - 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) Synonyms: Astronomical Unit |
| 1. | (networking) | au - The two character country code for Australia used in Internet domain names. | |
| 2. | (filename extension) | au - audio. |