- hotheaded, impulsive, impetuous, madcap, tearaway, brainish - characterized by undue haste and lack of thought or deliberation; "a hotheaded decision"; "liable to such impulsive acts as hugging strangers"; "an impetuous display of spending and gambling"; "madcap escapades"; (`brainish' is archaic)
Antonym: cautious (indirect, via incautious)