pith

Concise Oxford English Dictionary © 2008 Oxford University Press:
pith/pɪθ/

▶noun

• 1 spongy white tissue lining the rind of citrus fruits.

  ■ Botany the spongy cellular tissue in the stems and branches of many higher plants.

  ■ archaic spinal marrow.

• 2 the true nature or essence: the pith and core of socialism.

• 3 vigorous and concise expression.

▶verb

• 1 remove the pith from.

• 2 kill or immobilize (an animal) by piercing or severing the spinal cord.

– derivatives
pithless adjective.

– origin OE pitha, of W. Gmc origin.