att I. noun alsoat\ˈät\ (-s) Etymology: Siamese 1.: an old subsidiary coin of Siam worth 1/64 of a tical issued before 1868 in pewter and after that up to 1906 in copper 2.: a unit of value corresponding to the att < 2-att postage stamp > < 1/2-att coin > II. abbreviation 1. attaché 2. attached 3. attention 4.often capitalized attorney