A person who stirs up trouble or encourages others to rebel; also, a mechanical device that shakes or mixes things.
From Latin 'agitare' meaning 'to shake, stir, or drive,' combined with '-or' (one who does). The word has both social and mechanical meanings since the 1600s.
A washing machine has an 'agitator'—the part that shakes and swishes clothes—using the exact same meaning as a person who 'agitates' a group!
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