armor

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

• noun A defensive covering, as of metal, wood, or leather, worn to protect the body against weapons.
• noun A tough, protective covering, such as the bony scales covering certain animals or the metallic plates on tanks or warships.
• noun A safeguard or protection.
• noun The combat arm that deploys armored vehicles, such as tanks.
• noun The armored vehicles of an army.
• transitive verb To cover with armor.

from The Century Dictionary.

• To cover with armor or armor-plate.
• noun Defensive arms; any covering worn to protect the person against offensive weapons.
• noun The metallic sheathing, intended as a protection against projectiles, for a ship of war or the exposed face of a fortification. Figuratively, a defensive covering of any kind; that which serves as a protection or safeguard; a bulwark: used in zoology and botany of the protective envelop or cover of an animal or a plant, as the scales of a fish or the plates of a crocodile.
• noun In magnetism, same as armature
• noun In paleobotany, the thick covering or jacket which surrounds the woody axis of fossil cycadean trunks, consisting of the persistent leaf-bases and the copious ramentum which fills the interstices between them.

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

• noun Defensive arms for the body; any clothing or covering worn to protect one's person in battle.
• noun Steel or iron covering, whether of ships or forts, protecting them from the fire of artillery.
• noun the escutcheon of a person or family, with its several charges and other furniture, as mantling, crest, supporters, motto, etc.
• noun a water-tight dress or covering for a diver. See under Submarine.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun uncountable A protective layer over a body, vehicle, or other object intended to deflect or diffuse damaging forces.
• noun uncountable A natural form of this kind of protection on an animal's body.
• noun uncountable Metal plate, protecting a ship, military vehicle, or aircraft.
• noun countable A tank, or other heavy mobile assault vehicle.
• noun military, uncountable A military formation consisting primarily of tanks or other armoured fighting vehicles, collectively.
• noun hydrology, uncountable The naturally occurring surface of pebbles, rocks or boulders that line the bed of a waterway or beach and provide protection against erosion.
• verb transitive To equip something with armor or a protective coating or hardening.
• verb transitive To provide something with an analogous form of protection.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb equip with armor
• noun a military unit consisting of armored fighting vehicles
• noun protective covering made of metal and used in combat
• noun tough more-or-less rigid protective covering of an animal or plant