Pith (noun)

1. The soft spongelike tissue in the stems of most vascular plants, composing the cortex and located between the bark and the vascular tissue.
2. The core or central part of something.

Origin:

Middle english, from old english pitha; akin to old high german pfizzi pith.

Examples:

1. The pith of the orange is surrounded by a bitter layer.
2. The pith of the argument was that the system was flawed.
3. The pith of the cane can be cut away for use in making hats and baskets.
4. The pith of a tree is the central part, from which branches grow.
5. The pith of the story was that she was brave and determined.