unpremeditated
1. [ adjective ] not prepared or planned in advance
Examples:

"asked an unpremeditated question"

Related terms: unplanned
2. [ adjective ] not premeditated
Related terms: premeditated impulsive unplanned
Similar spelling:   unpredicted
  unpredictive
  unpredictable
  unprecedented
  unappareled
  unprecedentedly
  unpredictably