Matthew Meyers, age 15, of Providence, R. I., for his question:

WHAT IS AN ACHILLES HEEL?

An Achilles heel is an area, part, feature or trait that is solely  or especially vulnerable.  Achilles was the hero of Romer's "Iliad."

To protect her son Achilles, the sea nymph Thetis dipped the infant into the waters of the river Styx to make him invulnerable. Every part of the baby's body except the heal by which he was held, was made safe against injury.

Achilles grew to be a handsome young man and the swiftest of mortals. When the Trojan war broke out, Achilles went to Troy and became famous as the greatest of the Greek warriors.

The war went on and on.

Later Paris of Troy shot a poisoned arrow at Achilles. The arrow, guided by Apollo, entered the heel, the one part of his body that had not been dipped in the Styx, and Achilles died from the wound.

Today, the large tendon at the back of a person's heel is still known as the Achilles tendon.