Acid 10 : Medicine. A substance that has a pH of less than 7, which is neutral. Specifically, an acid has more free hydrogen ions (H+) than hydroxyl ions (OH-)
US Department of the Interior, US Geological Survey USGS, Water Science Glossary of Terms, http://ga.water.usgs.gov/edu/dictionary.html (Some of this information is courtesy of the Nevada Division of Water Resources - the detailed water glossary at VA, USA 2009. http://water.nv.gov/programs/planning/dictionary/) , (ND/ Flood - Amer) {491}
