impetuous (suomeksi)

harkitsematon (a)
äkkinäinen (a)
kiihkeä (a)
kiivas (a: describing one who makes arbitrary decisions)
kiihkeä (a: describing one who makes arbitrary decisions / characterized by sudden and violent force)
raju (a: describing one who makes arbitrary decisions / characterized by sudden and violent force)
äkkipikainen (a: describing one who makes arbitrary decisions)