Any salt or ester of nitric acid (HNO). The salts are inorganic compounds with ionic bonds, containing the nitrate ion (NO) and any cation. Many, particularly ammonium nitrate, are used as agricultural fertilizers (seesaltpeter). Their runoff in surface water and groundwater can cause serious illness in humans. The esters are organic compounds with covalent bonds, having the structure RONO, in which R represents an organic combining group such as methyl, ethyl, or phenyl.