• A chemical that gives off hydrogen ions in water and forms salts by combining with certain metals. Acids have a sour taste and turn certain dyes red. Some acids made by the body, such as gastric acid, can help the body work the way it should. An example of an acid is hydrochloric acid.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• A substance that yields hydrogen ions or protons in aqueous solutions; a substance capable of accepting a pair of electrons for the formation of a coordinate covalent bond; a substance whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water.
  NCI Thesaurus
  U.S. National Cancer Institute, 2021
• Substances whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals to form salts; yields hydrogen ions when dissolved in water, acts as a proton donor, and can accept a pair of electrons to form a covalent bond.
  CRISP Thesaurus
  National Institutes of Health, 2006
• Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. (Grant & Hackh's Chemical Dictionary, 5th ed)
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021