Etymology
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core (n.)

early 14c., "heart or inmost part of anything" (especially an apple, pear, etc.), of uncertain origin, probably from Old French cor, coeur "core of fruit, heart of lettuce," literally "heart," from Latin cor "heart," from PIE root *kerd- "heart."

Meaning "a central portion cut and removed" (as from a tree, soil, etc.) is from 1640s. Meaning "internal mold of a casting, which fills the space intended to be left hollow" is from 1730. Nuclear physics sense "portion of a reactor containing the nuclear fuel and where the reactions take place" is from 1949.

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core (v.)

"to remove the core of" (a fruit), mid-15c., from core (n.). Related: Cored; coring.

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corer (n.)

"instrument for cutting the core out of an apple or other fruit," 1796, agent noun from core (v.).

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hardcore 
also hard-core; 1936 (n.); 1951 (adj.); from hard (adj.) + core (n.). Original use seems to be among economists and sociologists, in reference to unemployables. Extension to pornography is attested by 1966. Also the name of a surfacing material.
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coke (n.1)

"fuel residue, solid product of the carbonization of coal,"an important substance in metallurgy, 1660s, a northern England dialect word, perhaps a variant of Middle English colke "core (of an apple), heart of an onion" (c. 1400), also "charcoal" (early 15c.), a word of uncertain origin. It seems to have cognates in Old Frisian and Middle Dutch kolk "pothole," Old English -colc, in compounds, "pit, hollow," Swedish dialectal kälk "pith." Perhaps the notion is the "core" of the coal, or "what is left in the pit after a fire."

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heartland (n.)
also heart-land, 1904, first recorded in geo-political writings of English geographer H.J. MacKinder (1861-1947), from heart (n.) in figurative sense "center, core" + land (n.).
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meltdown (n.)

by 1922 as "an act or the process of melting metal;" by 1956 in reference to the accidental melting of the core of a nuclear reactor, from the verbal phrase (1630s), from melt (v.) + down (adv.). Metaphoric extension "breakdown in self-control" is attested since 1979.

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trunnion (n.)

"either of two round projections of a cannon," 1620s, from French trognon "core of fruit, stump, tree trunk," from Old French troignon (14c.), probably from Latin truncus (see trunk (n.1)).

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know-nothing (n.)
1827, "ignoramus," from know (v.) + nothing. As a U.S. nativist political party, active 1853-56, the name refers to the secret society at the core of the party, about which members were instructed to answer, if asked about it, that they "know nothing." The party eventually merged into the Republican Party. Related: Know-nothingism.
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husk (n.)
late 14c., huske "dry, outer skin of certain fruits and seeds," of unknown origin. "A common word since c 1400 of which no earlier trace has been found" [OED]. Perhaps from Middle Dutch huuskyn "little house, core of fruit, case," diminutive of huus "house," or from an equivalent formation in English (see house (n.)).
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