The definition of acid is sour or sharp in taste, or having a pH of under 7 in chemistry.(noun)
Lemon juice and vinegar are each an example of an acid.
Acid is defined as something that has a sour taste, or something that has a pH of less than 7 in chemistry.(adjective)
Lemon is an example of an acid substance.
See acid in Webster's New World College Dictionary
Origin: L acidus, sour < IE base *a-, sharp, pointed > ear
See acid in American Heritage Dictionary 4
Origin: From Latin acidus, sour
Origin: , from acēre, to be sour; see ak- in Indo-European roots.
Learn more about acid