Old English piþa "pith of plants," also "essential part," from West Germanic *pithan- (cf. Middle Dutch pitte, Dutch pit, East Frisian pit), a Low German root of uncertain origin. Figurative sense was in Old English. Pith helmet (1889, earlier pith hat, 1884) so called because it is made from the dried pith of the Bengal spongewood.
"to kill by piercing the spinal cord," 1805, from pith (n.). Related: Pithed; pithing.
The soft inner substance of a hair.
Spinal cord or bone marrow. No longer in technical use.
Noun The soft, spongy tissue in the center of the stems of most flowering plants, gymnosperms, and ferns. Pith is composed of parenchyma cells. In plants that undergo secondary growth, such as angiosperms, the pith is surrounded by the vascular tissues and is gradually compressed by the inward growth of the vascular tissue known as xylem. In plants with woody stems, the pith dries out and often disintegrates as the plant grows older, leaving the stem hollow. See illustration at xylem.