adj. 25B6; adjective
he had an impulsive nature : IMPETUOUS, spontaneous, hasty, passionate, emotional, uninhibited; rash, reckless, foolhardy, unwise, madcap, devil-may-care, daredevil.
an impulsive decision : IMPROMPTU, snap, spontaneous, unpremeditated, spur-of-the-moment, extemporaneous; impetuous, precipitate, hasty, rash; sudden, ill-considered, ill-thought-out.
cautious, premeditated.