prosperity is the condition of thriving — most commonly economic well-being, and in the older and wider use, success and good fortune in anything desirable.
In economics the word names a sustained state rather than a moment: an economy is said to be in a period of prosperity when output, employment, and incomes are rising together, as distinct from the recovery that precedes it and the contraction that ends it. Applied to a household or a person it carries the same shape — not a sum held but a condition being maintained. The word also anchors the prosperity gospel, the twentieth-century Christian teaching that material wealth is evidence of divine favor, which is a doctrinal use rather than a separate sense.
English took the word around 1200 from Old French prosprete and Latin prosperitatem, "good fortune, wealth, success in anything good or desirable," from the adjective prosperus, "favorable, fortunate." Prosperus is traditionally traced to Old Latin pro spere, "according to expectation, according to one's hope," combining pro with the ablative of spes, "hope" — a root that also stands behind the English word speed in its older sense of success. The verb prosper follows in the mid-fourteenth century.
Prosperity is not 📝wealth, which is a stock of assets that can be held while the condition of thriving is absent, and not 📝abundance, which describes felt sufficiency and needs no economic referent at all. Its own history records how close the ideas once sat: thrift originally meant the fact of thriving, prosperity itself, before it narrowed to the habit of saving in the 1550s — which is why a 📝spendthrift is literally one who has spent their prosperity.