pith

Short definition from Wiktionary

Noun

1. 1
   The soft, spongy substance inside plant parts; specifically, the parenchyma in the centre of the roots and stems of many plants and trees.
2. 2
   The albedo (“whitish inner portion of the rind”) of a citrus fruit.
3. 3
   Senses relating to humans and animals: The soft tissue inside a human or animal body or one of their organs; specifically, the spongy interior substance of a horn or the shaft of a feather.
4. 4
   Senses relating to humans and animals: Chiefly of animals: the soft tissue inside a spinal cord; the spinal marrow; also, the spinal cord itself.
5. 5
   Senses relating to humans and animals: Synonym of diploe (“the thin layer of soft, spongy, or cancellate tissue between the bone plates which constitute the skull”).
6. 6
   Senses relating to humans and animals: The soft tissue of the brain.
7. 7
   The soft inner portion of a loaf of bread.
8. 8
   The central or innermost part of something; the core, the heart.
9. 9
   The essential or vital part of something; the essence.
10. 10
    Physical power or strength; force, might.
11. 11
    A quality of courage and endurance; backbone, mettle, spine.
12. 12
    The energy, force, or power of speech or writing; specifically, such force or power due to conciseness; punch, punchiness.
13. 13
    Chiefly in of (great) pith and moment: gravity, importance, substance, weight.
14. 14
    One divided by pi, that is, 1/π (approximately 0.31831…).

Verb

1. 1
   To render insensate or kill (an animal, especially cattle or a laboratory animal) by cutting, piercing, or otherwise destroying the spinal cord.
2. 2
   To extract the pith from (something or (figurative) someone).

Adjective

1. 1
   The ordinal form of the number pi (π; approximately 3.14159…).