optimism [M18th] Philosophers in the 18th century coined optimism for the theory that this is the best of all possible worlds. The word goes back to Latin optimum ‘best thing’. By the early 19th century it had gained wider currency, and was being used to mean a general tendency to hope for the best. The opposite, pessimism (from Latin pessimus ‘worst’), was also coined in the 18th century, when it meant ‘the worst possible state or condition’.