1843, usually said to be from Latin vim, accusative of vis "strength, force, power, vigor, energy," from Proto-Italic *wis-, traditionally from PIE root *weie- "to go after, pursue with vigor or desire," with noun derivatives indicating "force, power" (see gain (v.)) and related to the root of virile. But de Vaan seems to have doubts ("more easily explained from an original root noun"), and based on the early uses OED suggests the possibility that the English word is of "a purely inventive or interjectional origin."
