Definitions of impulsive:

• adjective:   without forethought

  Example: "Letting him borrow her car was an impulsive act that she immediately regretted"

• adjective:   proceeding from natural feeling or impulse without external stimulus

  Example: "An impulsive gesture of affection"

• adjective:   characterized by undue haste and lack of thought or deliberation

  Example: "Liable to such impulsive acts as hugging strangers"

• adjective:   determined by chance or impulse or whim rather than by necessity or reason
• adjective:   having the power of driving or impelling

  Example: "An impulsive force"