adj. 25B6; adjective
an impetuous decision : IMPULSIVE, rash, hasty, overhasty, reckless, heedless, foolhardy, incautious, imprudent, injudicious, ill-considered, unthought-out; spontaneous, impromptu, spur-of-the-moment, precipitate, precipitous, hurried, rushed.
an impetuous flow of water : TORRENTIAL, powerful, forceful, vigorous, violent, raging, relentless, uncontrolled; rapid, fast, fast-flowing.
considered, sluggish.