Adjective

• 1. not marked by the use of reason;

  "mindless violence"

  "reasonless hostility"

  "a senseless act"

• 2. not endowed with the capacity to reason;

  "a reasonless brute"

• 3. having no justifying cause or reason;

  "a senseless, causeless murder"

  "a causeless war that never had an aim"

  "an apparently arbitrary and reasonless change"