Synonyms of the word

unpremeditated

• adj. Performed, but not planned or thought out in advance; extemporaneous, but not unintentional.

impulsive

• adj. Having the power of driving or impelling; giving an impulse; moving; impellent.
• adj. Actuated by impulse or by transient feelings; inclined to make rapid decisions without due consideration.
• adj. (mechanics) Acting momentarily, or by impulse; not continuous – said of forces.
• n. That which impels or gives an impulse; an impelling agent.
• n. One whose behaviour or personality is characterized by being impulsive.

unplanned

• adj. unintentional; not intended.
• adj. spontaneous and not thought through in advance.
• adj. not having any structure or organization.