Merriam-Webster's Collegiate® Dictionary, 11th Edition
SHIELD
I. noun
Etymology: Middle English sheld, from Old English scield; akin to Old High German scilt shield and probably to Old English sciell shell Date: before 12th century a broad piece of defensive armor carried on the arm, one that protects or defends ; defense , dress shield ,
4. a device or part that serves as a protective cover or barrier, a protective structure (as a carapace, scale, or plate) of some animals, escutcheon , the Precambrian nuclear mass of a continent that is surrounded and sometimes covered by sedimentary rocks, something resembling a shield: as, apothecium , a police officer's badge, a decorative or identifying emblem,
II. transitive verb Date: before 12th century
1. to protect with or as if with a shield ; provide with a protective cover or shelter, to cut off from observation ; hide , forbid , see: defend shielder noun