newel (n.)

mid-14c., nouel, nowel, "pillar from which steps of a winding stair radiate, stone cut to form a step and a section of the central pillar of a spiral stair," from Old French noel, noiel, novel "knob, newel, kernel, stone" (Modern French noyau), from Vulgar Latin *nodellus "little knot," diminutive of Latin nodulus, itself a diminutive of nodus "knot" (from PIE root *ned- "to bind, tie").

Klein's sources suggest the French word may be from Gallo-Roman *nucale, from Latin nux "nut." The carpentry meaning "tall and more or less ornamental post at the top or bottom of a staircase" is from 1833 (newel-post in this sense is from 1798).