↑Smith's financial dictionary. Smith, Howard Irving. 1908. Income is defined as, "Revenue; the amount of money coming to a person or a corporation (usually interpreted as meaning annually) whether as payment for services or as interest or other profit from investment."
↑Webster's new modern English dictionary, illustrated. Webster, Noah. 1922. Income is defined as "the gain which proceeds from labor, business, property or capital; annual receipts of a person or corporation."
↑Barr, N. (2004). Problems and definition of measurement. In Economics of the welfare state. New York: Oxford University Press. pp. 121-124