Direct Opposites:
* Accidentally: This is the most direct opposite, implying something happened without intent.
* Unintentionally: This emphasizes the lack of a deliberate action.
Other Opposites:
* Carelessly: This implies a lack of thought or attention.
* Randomly: This suggests something happened without any specific goal in mind.
* Haphazardly: This indicates a lack of order or plan.
* Spontaneously: This emphasizes a lack of premeditation.
Example:
* Purposeful: "She made a purposeful stride towards the finish line."
* Opposite: "He accidentally knocked over the vase."
The best opposite for "purposefully" will depend on the specific situation and what you want to emphasize.