Etymology
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agitate (v.)

1580s, "to disturb," from Latin agitatus, past participle of agitare "to put in constant or violent motion, drive onward, impel," frequentative of agere "to set in motion, drive, drive forward," figuratively "incite to action; keep in movement, stir up" (from PIE root *ag- "to drive, draw out or forth, move").

Literal sense of "move to and fro, shake" is from 1590s. Meaning "to discuss, debate" is from 1640s, that of "keep (a political or social question) constantly in public view" is by 1828. Related: Agitated; agitating.

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agitated (adj.)
1610s, "set in motion," past-participle adjective from agitate (v.). Meaning "disturbed" is from 1650s; that of "disturbed in mind" is from 1756. Meaning "kept constantly in public view" is from 1640s.
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agitator (n.)
1640s, agent noun from agitate (v.); originally "elected representative of the common soldiers in Cromwell's army," who brought grievances (chiefly over lack of pay) to their officers and Parliament.

Political sense is first recorded 1734, and negative overtones began with its association with Irish patriots such as Daniel O'Connell (1775-1847). Historically, in American English, often with outside and referring to people who stir up a supposedly contented class or race. Latin agitator meant "a driver, a charioteer."
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churn (v.)

mid-15c., chyrnen, "to stir or agitate (milk or cream) to make butter," from churn (n.). Extended sense "shake or agitate violently" is from late 17c. Intransitive sense is from 1735. Related: Churned; churning. To churn out, of writing, "produce mechanically and in great volume" is from 1902.

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seismo- 
word-forming element meaning "earthquake," from Greek seismos "a shaking, shock; an earthquake," also "an extortion" (compare colloquial shake (someone) down), from seiein "to shake, agitate, sway; to quake, shiver" from PIE root *twei- "to agitate, shake, toss; excite; sparkle" (also source of Sanskrit tvesati "to excite; to be excited, inflame, sparkle," and Avestan words for "fears" and "fright, danger").
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insouciant (adj.)
1828, from French insouciant "careless, thoughtless, heedless," from in- "not" (see in- (1)) + souciant "caring," present participle of soucier "to care," from Latin sollicitare "to agitate" (see solicit). Related: Insouciantly.
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insouciance (n.)
1820, from French insouciance "heedless indifference or unconcern," from insouciant "carelessness, thoughtlessness, heedlessness," from in- "not" (see in- (1)) + souciant "caring," present participle of soucier "to care," from Latin sollicitare "to agitate" (see solicit).
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ripple (v.)

early 15c., riplen, "to crease, wrinkle;" 1660s, "to present a ruffled surface," of obscure origin, perhaps a frequentative of rip (v.), and compare rip (n.2) and rumple. Transitive sense, in reference to the surface of water, "cause to ripple, agitate lightly," is from 1786. Related: Rippled; rippling.

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fluster (v.)
early 15c. (implied in flostrynge), "bluster, agitate," probably from a Scandinavian source (compare Icelandic flaustr "bustle," flaustra "to bustle"), from Proto-Germanic *flaustra-, probably from PIE *pleud-, extended form of root *pleu- "to flow." Originally "to excite," especially with drink; sense of "to flurry, confuse" is from 1724. Related: Flustered; flustering; flustery. As a noun, 1710, from the verb.
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stir (v.)
Old English styrian "to stir, move; rouse, agitate, incite, urge" (transitive and intransitive), from Proto-Germanic *sturjan (source also of Middle Dutch stoeren, Dutch storen "to disturb," Old High German storan "to scatter, destroy," German stören "to disturb"), from PIE *(s)twer- (1) "to turn, whirl" (see storm (n.)). Related: Stirred; stirring. Stir-fry (v.) is attested from 1959.
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