Unprovoked (adjective)

1. Done or occurring without any obvious cause or reason.
2. Not caused by or resulting from a provocation.

Origin:

From the latin word 'inprovocatus' meaning 'not provoked'.

Examples:

1. The attack was unprovoked and caught everyone by surprise.
2. She received an unprovoked compliment from a stranger.
3. The loud noise was unprovoked and startled everyone in the room.
4. The police are investigating an unprovoked assault on a pedestrian.
5. The dog barked unprovoked at the mailman.