"Chance of mischief". This definition comes from Johnson's "Word reference of the English Language" (1755), and has been generally reworded, including "plausibility of misfortune" [5] or "likelihood of undesirable events".[7] "Vulnerability regarding misfortune". This definition comes from Willett's "Monetary Theory of Risk and Insurance" (1901).[8] This connections "hazard" to "vulnerability", which is a more extensive term than possibility or likelihood. "Quantifiable vulnerability". This definition comes from Knight's "Hazard, Uncertainty and Profit" (1921).[9] It permits "hazard" to be utilized similarly for positive and adverse results. In protection, hazard implies circumstances with obscure results yet known likelihood distributions. [10] "Instability of return". Proportionality among hazard and fluctuation of return was first recognized in Markovitz's "Portfolio Selection" (1952).[11] In finance, unpredictability of return is regularly likened to risk.[12]