Synonyms for impetuous

These adjectives describe abruptness or lack of deliberation. Impetuous suggests forceful impulsiveness or impatience: “[a race driver who was] flamboyant, impetuous, disdainful of death” (Jim Murray).
Heedless implies carelessness or lack of responsibility or proper regard for consequences: “Hobbling down stairs with heedless haste, I set my foot full in a pail of water” (Richard Steele).
Hasty and headlong both stress hurried, often reckless action: “Hasty marriage seldom proveth well” (Shakespeare). “In his headlong flight down the circular staircase, … [he] had pitched forward violently, struck his head against the door to the east veranda, and probably broken his neck” (Mary Roberts Rinehart).
Precipitate suggests impulsiveness and lack of due reflection: a precipitate decision.
Sudden applies to what becomes apparent abruptly or unexpectedly: is given to sudden paroxysms of anger.