shield n.

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).

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.