Etymology
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perfuse (v.)

early 15c., perfusen, "to wash away;" 1520s, "to sprinkle, pour or spread over or through," from Latin perfusus, past participle of perfundere "to pour over, besprinkle," from per (see per) + fundere "to pour, melt" (from nasalized form of PIE root *gheu- "to pour").

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perchance (adv.)

"perhaps, possibly, maybe," mid-14c., parchaunce, from Old French par cheance, literally "by chance." With Latin per substituted c. 1400 for French cognate par. See per + chance (n.).

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permute (v.)

late 14c., permuten, "to change one for another, to interchange," from Old French permuter and directly from Latin permutare "to change thoroughly," from per "thoroughly" (see per) + mutare "to change" (from PIE root *mei- (1) "to change, go, move"). The mathematical sense is from 1878 (see permutation).

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segregate (v.)

1540s, "separate (someone or something) from a generally body or class of things," from Latin segregatus, past participle of segregare "set apart, lay aside; isolate; divide," literally "separate from the flock," from *se gregare, from se "apart from" (see se-) + grege, ablative of grex "herd, flock" (from PIE root *ger- "to gather").

Originally often with reference to the religious notion of separating the flock of the godly from the sinners, later scientifically in reference to classifications. In modern social context, "to force or enforce racial separation and exclusion," by 1898. Intransitive sense of "separate, go apart" is by 1863. Related: Segregated; segregating.

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secession (n.)
Origin and meaning of secession

1530s, from Latin secessionem (nominative secessio) "a withdrawal, separation; political withdrawal, insurrection, schism," noun of action from past-participle stem of secedere "go away, withdraw, separate; rebel, revolt," from se- "apart" (see se-) + cedere "to go" (from PIE root *ked- "to go, yield").

Originally in a Roman historical context, "temporary migration of plebeians from the city to compel patricians to address their grievances." Modern use is by 1650s in reference to "act of withdrawing from a religious or political union."

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mil (n.)

1721, in per mil "per thousand," from Latin mille "thousand" (see million); compare percent. As a unit of length for diameter of wire (equal to .001 of an inch) it is attested from 1891; as a unit of angular measure it is recorded by 1907.

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mpg 
originally m.p.g., abbreviation of miles per gallon, attested from 1912.
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pervasive (adj.)

tending or having the power to pervade," "1750, with -ive + Latin pervas-, past-participle stem of pervadere "spread or go through," from per "through" (from PIE root *per- (1) "forward," hence "through") + vadere "to go" (see vamoose). Related: Pervasively; pervasiveness.

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ppm 

also p.p.m., abbreviation of parts per million, attested by 1913.

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select (adj.)

1560s, "chosen on account of special excellence or fitness," from Latin selectus, past participle of seligere "choose out, single out, select; separate, cull," from se- "apart" (see se-) + legere "to gather, select" (from PIE root *leg- (1) "to collect, gather").

"Carefully picked," hence "choice, of special excellence" (by 1580s). Related: Selectly; selectness. The noun meaning "a selected person or thing, that which is choice" is recorded from c. 1600.

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