pillar, post, cylinder, support
柱 centers on a vertical structural element that holds something up: a pillar, post, or column. The cylinder sense comes from the typical shape of such supports.
柱 combines 木 (tree, wood) with 主, which likely contributes the sound and the idea of a main upright support. The character originally referred to a wooden pillar.
A wooden 木 main 主 support: picture a thick wooden pillar holding up the main beam of a building.
For チュウ, imagine a pillar in the middle of a room that you choose to lean against: choose -> チュウ, and the pillar supports you.
pillar; post
utility pole; power pole; telephone pole; telegraph pole
prop; stay; support; brace; fulcrum
person who died for a cause
spinal column; vertebral column; spine
column; shaft; cylinder
central pillar (of a building)
icicle
telephone pole
adductor muscle
stone pillar
prism
shape of a pillar or column
gatepost; pier
upright-floating tea stalk (considered a lucky omen)
iron pole
pillar of fire; blazing column
triangular prism
wall clock; grandfather clock
mast