Etymology
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when (adv.)
Old English hwænne, hwenne, hwonne, from Proto-Germanic *hwan- (source also of Old Saxon hwan, Old Frisian hwenne, Middle Dutch wan, Old High German hwanne, German wann "when," wenn "if, whenever"), from pronominal stem *hwa-, from PIE root *kwo-, stem of relative and interrogative pronouns. Equivalent to Latin quom, cum. As a conjunction in late Old English. Say when "tell me when to stop pouring you this drink" is from 1889.
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whence (adv., conj.)
early 13c., whennes, with adverbial genitive -s, from Old English hwanone, related to hwænne (see when). Spelling with -ce (1520s) reflects the voiceless pronunciation.
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*kwo- 
also *kwi-, Proto-Indo-European root, stem of relative and interrogative pronouns.

It forms all or part of: cheese (n.2) "a big thing;" cue (n.1) "stage direction;" either; hidalgo; how; kickshaw; neither; neuter; qua; quality; quandary; quantity; quasar; quasi; quasi-; query; quib; quibble; quiddity; quidnunc; quip; quodlibet; quondam; quorum; quote; quotidian; quotient; ubi; ubiquity; what; when; whence; where; whether; which; whither; who; whoever; whom; whose; why.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit kah "who, which;" Avestan ko, Hittite kuish "who;" Latin quis/quid "in what respect, to what extent; how, why," qua "where, which way," qui/quae/quod "who, which;" Lithuanian kas "who;" Old Church Slavonic kuto, Russian kto "who;" Old Irish ce, Welsh pwy "who;" Old English hwa, hwæt, hwær, etc.
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meteoroid (n.)

"rock or metallic mass floating in space," which becomes a meteor when it enters Earth's atmosphere and a meteorite when it strikes, 1865, formed in English from meteor + -oid.

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possum (n.)

American marsupial mammal, 1610s, shortened form of opossum (q.v.). It is nocturnal, omnivorous, and when caught or threatened with danger feigns death; hence the phrase play possum "feign death when threatened," attested by 1822.

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white feather (n.)
as a symbol of cowardice, 1785, said to be from the time when cock-fighting was respectable, and when the strain of game-cock in vogue had no white feathers, so that "having a white feather, is proof he is not of the true game breed" [Grose].
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forenoon (n.)
"the morning," especially the latter part of it, when business is done, c. 1500, from fore- + noon.
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off-season (n.)

1848, "a period when business is down," from off- (adj.) (see off (prep.)) + season (n.).

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