Meaning

• The soft, spongy substance in the center of the stems of many plants and trees.

• The spongy interior substance of a feather or horn.

• The spinal cord; the marrow.

• The albedo of a citrus fruit.

• The essential or vital part; force; energy; importance.

  "The pith of my idea is that people should choose their own work hours."

• Power, strength, might.

Meaning

• To extract the pith from (a plant stem or tree).

• To kill (especially cattle or laboratory animals) by cutting or piercing the spinal cord.