impetus comes from Latin impetus ('attack, assault, impulse'), from impetere ('to attack'), from in- ('toward') + petere ('to seek, rush at'). Morphologically, the prefixed shape matters: the initial element belongs to the recorded formation and helps explain the modern form's surface analysis. In present English, the noun sense is "a driving force or stimulus that makes something happen", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as impetuous, petition, compete, and appetite, and in derivatives such as impetuous. Its semantic neighborhood includes stimulus, impulse, momentum, and drive, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Latin impetus, Latin petere, and Proto-Indo-European *peth₂-.