(armor) A broad piece of defensive armor, carried on the arm, formerly in general use in war, for the protection of the body.
1599: Knocks go and come; God's vassals drop and die; And sword and shield, In bloody field, Doth win immortalfame. — William Shakespeare, Henry V, Act III, Scene II, line 8.
1592: Go muster men. My counsel is my shield; We must be brief when traitorsbrave the field. — William Shakespeare, Richard III, Act 4, Scene 3, line 56.
Figuratively, one who protects or defends.
1611: Fear not, Abram: I am thyshield, and thy exceeding great reward. The Holy Bible, King James Version, Genesis 15:1.
(botany) In lichens, a hardened cup or disk surrounded by a rim and containing the fructification, or asci.