1650s, "active operation;" 1670s, "a mode of exerting power or producing effect," from Medieval Latin agentia, abstract noun from Latin agentem (nominative agens) "effective, powerful," present participle of agere "to set in motion, drive forward; to do, perform," figuratively "incite to action; keep in movement" (from PIE root *ag- "to drive, draw out or forth, move"). Meaning "establishment where business is done for another" first recorded 1861.
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