Etymology
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shield (n.)
Old English scield, scild "shield; protector, defense," literally "board," from Proto-Germanic *skelduz (source also of Old Norse skjöldr, Old Saxon skild, Middle Dutch scilt, Dutch schild, German Schild, Gothic skildus), from *skel- "divide, split, separate," from PIE root *skel- (1) "to cut." Perhaps the notion is of a flat piece of wood made by splitting a log. Shield volcano (1911) translates German Schildvulkan (1910). Plate tectonics sense is from 1906, translating Suess (1888).
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shield (v.)
Old English gescildan, from the root of shield (n.). Related: Shielded; shielding. Compare German scilden.
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windshield (n.)
1902, from wind (n.1) + shield (n.). U.S. alternative to British windscreen (which is attested from 1905 in this sense).
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sheldrake (n.)
early 14c., from sheld- "variegated" + drake "male duck." First element cognate with Middle Dutch schillede "separated, variegated," West Flemish schilde, from schillen (Dutch verschillen "to make different"), from Proto-Germanic *skeli-, from PIE root *skel- (1) "to cut." This is the origin considered most likely, though English sheld by itself is a dialect word attested only from c. 1500. OED finds derivation from shield (n.), on resemblance to the patterns on shields, "improbable."
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shoulder (n.)
Old English sculdor "shoulder," from West Germanic *skuldro (source also of Middle Dutch scouder, Dutch schouder, Old Frisian skoldere, Middle Low German scholder, Old High German scultra, German Schulter), of unknown origin, perhaps related to shield (n.). Meaning "edge of the road" is attested from 1933. Cold shoulder (Nehemiah ix.29) translates Latin humerum recedentum dare in Vulgate (but see cold shoulder). Shoulder-length, of hair, is from 1951.
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shelter (n.)
1580s, "structure affording protection," possibly an alteration of Middle English sheltron, sheldtrume "roof or wall formed by locked shields," from Old English scyldtruma, from scield "shield" (see shield (n.)) + truma "troop," related to Old English trum "strong, firm, stable," from Proto-Germanic *trum-, from PIE *dru-mo-, suffixed form of root *deru- "be firm, solid, steadfast."

If so, the original notion is of a compact body of men protected by interlocking shields. OED finds this "untenable" and proposed derivation from shield + -ture. Figurative sense is recorded from 1580s; meaning "temporary lodging for homeless poor" is first recorded 1890 in Salvation Army jargon; sense of "temporary home for animals" is from 1971. Related: Shelterless.
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shilling (n.)
Old English scilling, a coin consisting of a varying number of pence (on the continent, a common scale was 12 pennies to a shilling, 20 shillings to a pound), from Proto-Germanic *skillingoz- (source also of Old Saxon, Danish, Swedish, Old Frisian, Old High German skilling, Old Norse skillingr, Dutch schelling, German Schilling, Gothic skilliggs).

Some etymologists trace this to the root *skell- "to resound, to ring," and others to the root *(s)kel- (1) "to cut" (perhaps via sense of "shield" from resemblance or as a device on coins; see shield (n.)). The ending may represent the diminutive suffix -ling, or Germanic -ing "fractional part" (compare farthing). Old Church Slavonic skulezi, Polish szeląg, Spanish escalin, French schelling, Italian scellino are loan-words from Germanic.
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*skel- (1)
also *kel-, Proto-Indo-European root meaning "to cut."

It forms all or part of: coulter; cutlass; half; halve; scale (n.1) "skin plates on fish or snakes;" scale (n.2) "weighing instrument;" scalene; scallop; scalp; scalpel; school (n.2) "group of fish;" sculpture; shale; sheldrake; shelf; shell; shield; shoal (n.2) "large number;" skoal; skill.

It is the hypothetical source of/evidence for its existence is provided by: Latin culter "knife," scalpere "to cut, scrape;" Old Church Slavonic skolika "mussel, shell," Russian skala "rind, bark," Lithuanian skelti "split," Old English scell "shell," scalu "drinking cup, bowl, scale of a balance."
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ecu (n.)
old French silver coin, 1704, from French écu, "a shield," also the name of a coin, from Old French escu (12c.) "shield, coat of arms," also the name of a coin with three fleur-de-lys stamped on it as on the shield, formerly escut, from Latin scutum "shield" (see escutcheon). First issued by Louis IX (1226-1270); so called because the shield of France was imprinted on them.
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umbo (n.)
"boss of a shield," 1921, from Latin umbo "shield-boss, knob, projection."
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