Etymology
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van de Graaff 
in reference to an electrostatic charge generator, 1934, named for U.S. physicist R.J. van de Graaff (1901-1967).
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van (n.1)
"front part of an army or other advancing group," c. 1600, shortening of vanguard.
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van (n.2)
"covered truck or wagon," 1829, shortening of caravan. Century Dictionary suggests this was perhaps regarded as *carry-van.
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de 

Latin adverb and preposition of separation in space, meaning "down from, off, away from," and figuratively "concerning, by reason of, according to;" from PIE demonstrative stem *de- (see to). Also a French preposition in phrases or proper names, from the Latin word.

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de- 

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

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Van Allen 
name of radiation belts around the Earth (and certain other planets), 1959, from U.S. physicist James A. Van Allen (1914-2006), who reported them in 1958.
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de jure 

Latin, literally "of law," thus "legitimate, lawful, by right of law, according to law." Jure is ablative of ius "law" (see de +  just (adj.)).

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de rigueur 
1849, French, literally "of strictness," thus "according to obligation of convention." See rigor.
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de minimis 
Latin, literally "of little things," thus, "so minor as to not be worth regarding."
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de-accession (v.)

also deaccession, "remove an entry for an item from the register of a museum, library, etc." (often a euphemism for "to sell"), by 1968, from de- "off, away" + accession, which had been used since 1887 in library publications as a verb meaning "to add to a catalogue." Related: De-accessioned; de-accessioning.

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