madcap

(noun) a reckless impetuous irresponsible person. Synonyms: daredevil, hothead, swashbuckler, lunatic, harum-scarum.

(adj) characterized by undue haste and lack of thought or deliberation. Synonyms: hotheaded, impulsive, impetuous, tearaway(prenominal), brainish. Examples: "A hotheaded decision." "Liable to such impulsive acts as hugging strangers." "An impetuous display of spending and gambling." "Madcap escapades"; (`brainish' is archaic)."