shield

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A broad piece of armor made of rigid material and strapped to the arm or carried in the hand for protection against hurled or thrusted weapons.
• noun A person or thing that provides protection.
• noun A protective device or structure, as.
• noun A steel sheet attached to an artillery piece to protect gunners from small-arms fire and shrapnel.
• noun Physics A wall or housing of concrete or lead built around a nuclear reactor to prevent the escape of radiation.
• noun Electronics A structure or arrangement of metal plates or mesh designed to protect a piece of electronic equipment from electrostatic or magnetic interference.
• noun A pad worn, as at the armpits, to protect a garment from perspiration.
• noun A sanitary napkin.
• noun Zoology A protective plate or similar hard outer covering; a scute or scutellum.
• noun Something that resembles a shield, as.
• noun An escutcheon.
• noun A decorative emblem that often serves to identify an organization or a government.
• noun A police officer's badge.
• noun Geology The ancient, stable, interior layer of continents composed of primarily Precambrian igneous or metamorphic rocks.
• intransitive verb To protect from being attacked, exposed to danger, or subjected to difficulty: synonym: defend.
• intransitive verb To cover up; conceal.
• intransitive verb To act or serve as a shield or safeguard.

from The Century Dictionary.

• To protect, defend, or shelter from danger, calamity, distress, annoyance, or the like: as, to shield one from attack; to shield one from the sun; to shield a criminal.
• To ward off.
• To forfend; forbid; avert.
• To act or serve as a shield; be a shelter or protection.
• noun A guard placed over or in front of rapidly moving machinery, especially over cutters such as saws and planes, to protect the workmen from accidents.
• noun A guard placed around belting where it passes through a floor, or around gears to prevent clothing of workmen or passers-by from becoming entangled
• noun A covering over bearings and shafts of grinding machinery to keep grit and dust from working into the contact-surfaces.
• noun A guard placed on an exposed shaft, and turning loosely with it, to prevent injury from accidental contact with the revolving mass.
• A frame or rounded plate made of wood, metal, hide, or leather, carried by warriors on the arm or in the hand, as a defense, from remote antiquity until the perfection of firearms rendered it more an encumbrance than a safeguard, and by savage peoples to the present day.
• Anything that protects or is used as a protection.
• A fender-plate attached to the share of a corn-plow to prevent clods from rolling on to the young plants.
• In zoology:
• A protective or defensive plate, buckler, or cuirass, of some determinate size, shape, or position; a scute, scutum, or scutellum; a lorica; a carapace: as, the shields or bucklers of a ganoid fish; the shields of a turtle, an armadillo, etc. See cuts under carapace, leaf-roller, scale, armadillo, and coluber.
• Some part, place, or mark likened to a shield; a thyroid formation. See cut under larynx.
• In dressmaking, a piece or strip of some repellent fabric used to protect a dress from mud, perspiration, etc.: as, a skirt-shield; an arm-shield.
• Figuratively, a shelter, protection, or defense; a bulwark.
• In botany, any flat, buckler-like body that is fixed by a stalk or pedicel from some part of the under surface, as the apothecium in certain lichens. (See apothecium.)
• In heraldry:
• The shield-shaped escutcheon used for all displays of arms, except when borne by women and sometimes by clergymen. See escutcheon and lozenge.
• A bearing representing a knightly shield.
• A French crown (in French, écu), so called from its having on one side the figure of a shield.
• The semi-transparent skin of the sides of a boar-pig, which is of considerable thickness, affording shield-like protection against the attacks of an adversary: apparently used formerly to furnish a shield for burlesque or mimic contests.
• A breed of domestic pigeons, of which there are four varieties, black, red, blue, and silver.
• More properly, a mantlet or wooden bulwark for crossbowmen and the like.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To cover with, or as with, a shield; to cover from danger; to defend; to protect from assault or injury.
• transitive verb To ward off; to keep off or out.
• transitive verb obsolete To avert, as a misfortune; hence, as a supplicatory exclamation, forbid!
• noun A broad piece of defensive armor, carried on the arm, -- formerly in general use in war, for the protection of the body. See buckler.
• noun Anything which protects or defends; defense; shelter; protection.
• noun Figuratively, one who protects or defends.
• noun (Bot.) In lichens, a Hardened cup or disk surrounded by a rim and containing the fructification, or asci.
• noun (Her.) The escutcheon or field on which are placed the bearings in coats of arms. Cf. Lozenge. See Illust. of Escutcheon.