An Etymological Dictionary of Astronomy and Astrophysics

1. A broad piece of armor carried on the arm as a defense against swords, arrows, etc.
   

2. A person or thing that protects or defends.
   → heat shield; → ozone shield; → self-shielding; → shielding effect.

Etymology (EN): M.E. shelde, from
O.E. scield, scild, related to sciell “seashell, eggshell;”
cf. Du. schild, Ger. Schild, Goth. skildus; PIE base *(s)kel- “to cut.”

Etymology (PE): Separ “shield,” from Mid.Pers. spar “shield;” cf. Skt. phalaka- “board, lath, leaf, shield,” phálati “(he) splits;” Gk. aspalon “skin, hide,” spolas “flayed skin,” sphalassein “to cleave, to disrupt;”
O.H.G. spaltan “to split;” Goth. spilda “board;” PIE base *(s)p(h)el- “to split, to break off.”