1570s, "spiny, full of sharp points, armed with prickles" (originally of holly leaves), from prickle (n.) + -y (2). Figurative sense of "irritable, quick to anger" is recorded by 1862. Prickly heat "inflammatory disorder of the sweat glands" is from 1736, so called for the sensation; prickly pear, of the fruit of a certain cactus, is from 1760 (earlier prickle pear, 1610s). Related: Prickliness.
Middle English shelden "protect, defend, or shelter (someone or something) from danger or harm; defend by interposition," from Old English gescildan, from the root of shield (n.). Related: Shielded; shielding. Compare German scilden.
Middle English sheld, "frame or rounded plate of wood, metal, etc., carried by an warrior on the arm or in the hand as defense," from Old English scield, scild "shield; protector, defender," originally "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."
The IE sense evolution of that proposal is uncertain; the ancient notion is perhaps a flat piece of wood made by splitting a log, but Boutkan writes, "it seems more probable to me that the word designated a means of protection, i.e. a separation between the fighter and the enemy."
Shield usually meant a larger defensive device, covering much of the body, as opposed to a buckler. Shield volcano (1911) translates German Schildvulkan (1910). The plate tectonics sense of shield as "large, stable mass of Achaean rock forming a continental nucleus" is by 1906, translating Suess (1888).
Old English fearn "fern," from Proto-Germanic *farno- (source also of Old Saxon farn, Middle Dutch vaern, Dutch varen, Old High German farn, German Farn). Watkins and other sources propose an etymology on the notion of "having feathery fronds" from a possible PIE *por-no- "feather, wing" (source also of Sanskrit parnam "feather, leaf;" Lithuanian papartis "fern;" Russian paporot'; Greek pteris "fern"), a proposed suffixed form of the root *per- (2) "to lead, pass over," on the notion of "that which carries a bird in flight."
The plant's ability to appear as if from nothing accounts for the ancient belief that fern seeds conferred invisibility (1590s). Filicology "science or study of ferns" (1848) is from Latin filix "fern."
"freckles, spots or blemishes on the body" (late 14c.), of unknown origin. Related: Fern-tickled "having spots or blemishes on the skin."
"boss of a shield," 1921, from Latin umbo "shield-boss, knob, projection."
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.
"coarse fern," c. 1300, a northern England word, probably from a Scandinavian source (compare Danish bregne, Swedish bräken "fern"), from Proto-Germanic *brak- "undergrowth, bushes," from PIE root *bhreg- "to break" on the notion of "that which impedes motion" [Watkins].
"thicket; place overgrown with bushes, brambles, or brushwood," mid-15c., originally "fern-brake, thicket of fern," perhaps from or related to Middle Low German brake "rough or broken ground," from the root of break (v.). Or, more likely, from Middle English brake "fern" (c. 1300), from Old Norse (compare Swedish bräken, Danish bregne), and related to bracken. In the U.S., the word was applied to cane thickets.