sheldrake n.

"male of the duck," c. 1300, unrecorded in Old English, but it might have existed, from West Germanic *drako (source also of Low German drake, second element of Old High German anutrehho, German Enterich, dialectal German Drache).

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."

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).