IPA: //ˈædʒɪˌteɪtə//
KK: /ˈædʒɪˌteɪtər/
A person or device that stirs or shakes things, often used to describe someone who encourages others to take action, especially in politics or social issues.
The agitator rallied the crowd to demand change.
Agitator is formed from "agere" (meaning to drive or to do) and the suffix "-tor" (meaning one who). The word describes one who drives or stirs up action, often in a political or social context.
Think of someone who 'drives' ('agere') others to take action — that's what an agitator does.