impulsive in WordNet English dictionary

1. 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)
   hotheaded  impulsive  impetuous  madcap  tearaway  brainish 
   
2. determined by chance or impulse or whim rather than by necessity or reason
   "a capricious refusal"; "authoritarian rulers are frequently capricious"; "the victim of whimsical persecutions"
   capricious  impulsive  whimsical 
   
3. having the power of driving or impelling
   "a driving personal ambition"; "the driving force was his innate enthusiasm"; "an impulsive force"
   driving  impulsive 
   
4. proceeding from natural feeling or impulse without external stimulus
   "an impulsive gesture of affection"
   impulsive  unprompted 
   
5. without forethought
   "letting him borrow her car was an impulsive act that she immediately regretted"
   impulsive