See Metaphysics, No. 3.

ONYCOMANCY; or, as some write it, ONYMANCY; a kind of divination by means of the nails of the fingers.—The word is formed from the Greek ὄνυξ "nail," and μαντεία, "divination."

The ancient practice was to rub the nails of a youth with oil and root, or wax; and to hold up the nails thus smeared against the sun.—Upon them were supposed to appear figures or characters, which showed the thing required.