Impetuous is a synonym of impulsive that describes a person who is acting without thought, or an action that is done without thought.

// That impetuous decision could've cost us everything we worked so hard for.

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“She takes off, impetuous and alone, for a cross-country trip, seeking some kind of self-understanding as she ultimately lands in the forests of California’s redwood country, finding both a sanctuary and, whether she knows it or not, a bucket-list tribute to her late son.” — Greg Evans, Deadline, 28 Apr. 2025

Impetuous types make impetuous decisions: they leap before they look, put carts before horses, count their chickens before even the tiniest of cracks appear on the eggs. In other words, they’re impulsive. The etymology of impetuous is also impulsive but in a literal way: it traces back to the Latin word impetus, meaning “impulse, driving force,” as well as “assault.” English impetus, also meaning “impulse, driving force” (among other things), has the same source.