pillar vs newel

pillar and newel both are nouns.

Word	Noun	Adjective	Verb	Adverb
pillar	Yes	No	No	No
newel	Yes	No	No	No

As nouns, newel is a hyponym of pillar; that is, newel is a word with a more specific, narrower meaning than pillar:

pillar: (architecture) a tall vertical cylindrical structure standing upright and used to support a structure
newel: the central pillar of a circular staircase

Other hyponyms of pillar include atlas, telamon, caryatid, pilaster, pile, piling, spile, stilt, support column.

pillar (noun)	newel (noun)
(architecture) a tall vertical cylindrical structure standing upright and used to support a structure	the central pillar of a circular staircase
a vertical cylindrical structure standing alone and not supporting anything (such as a monument)	the post at the top or bottom of a flight of stairs; it supports the handrail
a fundamental principle or practice
a prominent supporter
anything that approximates the shape of a column or tower