impurity
n.a small amount of something that is not pure. It can be a dirt particle in water or a bad quality in a person's character.
n.a substance that is not pure; an element or compound that is present in a material in an undesired or unintended state. Often used metaphorically to describe a flaw in a person's character or a process.
“The water was clear, but it still contained a small impurity.”
“The chemist used a special filter to remove any impurity from the liquid before the final test.”
“While the diamond was nearly flawless, a microscopic impurity in the crystal lattice caused it to refract light in a slightly different way than a pure specimen.”
“Extreme heat would destroy their structure and produce unwanted impurities.”
From impure + -ity. From Middle French impurité, from Latin impuritas.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.