The word 'windfall' is a transparent compound from Old English elements, originally describing fruit, especially apples, knocked down by the wind. This literal sense reflects a practical event for foragers or farmers, where such fruit was an unexpected, unearned bounty. Over time, the core concept of an unexpected gain, detached from effort, was metaphorically extended to financial contexts. The term's logic perfectly captures the transition from a concrete, natural event to an abstract economic one, embodying the idea of a sudden, fortunate acquisition.

Structure: wind (air in motion) + fall (to drop) - wind: Old English wind, of Germanic origin; from an Indo-European root shared by Latin ventus. The functional role is a noun used attributively to describe the cause. - fall: Old English feallan, of Germanic origin; related to Dutch vallen and German fallen. The functional role is a noun derived from the verb, indicating the event or result of dropping.