Etymology
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impulse (n.)
early 15c., "an act of impelling, a thrust, push," from Latin impulsus "a push against, pressure, shock," figuratively "incitement, instigation," past participle of impellere "to strike against, push against," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + pellere "to push, drive" (from PIE root *pel- (5) "to thrust, strike, drive"). Meaning "a stimulus in the mind to action, arising from some state or feeling" is first recorded 1640s. As an adjective, in reference to purchases made on impulse, 1955 (in impulse buyer).
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impulsive (adj.)

early 15c., originally in reference to medicine that reduces swelling or humors, from Medieval Latin impulsivus, from Latin impuls-, past participle stem of impellere "strike against, push against" (see impel). Meaning "having the property of impelling" (of force, cause, energy, etc.) is from c. 1600. Of persons, "rash, characterized by impulses," from 1847, from impulse. Earlier, at least once, in reference to maniacs:

The impulsive insane are often irritable, restless and jealous. Sometimes they have delusions, and sometimes not. Their delusions frequently seem to have no connection with their outbreaks of violence. They are often the best and at the same time the most dangerous class of patients in the asylums. They have little of the charity of the world, are most likely to be punished for their offences, and yet have the least control over their conduct. ["Impulsive and Homicidal Insanity," Boston Medical and Surgical Journal, April 19, 1843]
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*pel- (5)
Proto-Indo-European root meaning "to thrust, strike, drive."

It forms all or part of: anvil; appeal; catapult; compel; dispel; expel; felt (n.) "unwoven fabric matted together by rolling or beating;" filter; filtrate; impel; impulse; interpellation; interpolate; peal; pelt (v.) "to strike (with something);" polish; propel; pulsate; pulsation; pulse (n.1) "a throb, a beat;" push; rappel; repeal; repel; repousse.

It is the hypothetical source of/evidence for its existence is provided by: Greek pallein "to wield, brandish, swing," pelemizein "to shake, cause to tremble;" Latin pellere "to push, drive;" Old Church Slavonic plŭstĭ.
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neurotransmitter (n.)

"chemical substance which transmits an impulse from one nerve fiber to another or others," 1959, from neuro- + transmitter.

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sforzando (adj.)

"with sudden energy or impulse," 1801, from Italian sforzando, present participle of sforza "to force," from Vulgar Latin *exfortiare "to show strength" (see effort).

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projectile (adj.)

1690s, "caused by impulse;" 1715, "impelling, throwing;" see project (v.) + -ile. By 1865 as "capable of being thrust forward." Projectile vomiting is attested from 1985. 

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pyromaniac (adj.)

"of, pertaining to, characterized by, or affected with pyromania," 1855, from pyromania. As a noun from 1861, "person possessed of an irresistible impulse to burn things." Related: Pyromaniacal.

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premotion (n.)

motion or impulse given beforehand," "1640s, from Medieval Latin praemotionem (nominative praemotio), noun of action from past-participle stem of Late Latin praemovere, from prae "before" (see pre-) + movere "to move" (from PIE root *meue- "to push away").

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momentum (n.)

1690s in the scientific use in mechanics, "product of the mass and velocity of a body; quantity of motion of a moving body," from Latin momentum "movement, moving power" (see moment). Figurative use, "force gained by movement, an impulse, impelling force," dates from 1782.

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accord (n.)
Origin and meaning of accord
late 13c., "agreement, harmony of opinions," accourd, acord, from Old French acorde, acort "agreement, alliance," a back-formation from acorder "reconcile, agree, be in harmony" (see accord (v.)). Meaning "will, voluntary impulse or act" (as in of one's own accord) is from mid-15c.
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