What does "pillar" mean?

Additional senses

1. 2.Figuratively, that which resembles such a pillar in appearance, character, or office; a supporter or mainstay; as, the Pillars of Hercules; a pillar of the state. "You are a well-deserving pillar." Shak. By day a cloud, by night a pillar of fire. Milton.
2. 3.(R. C. Ch.) A portable ornamental column, formerly carried before a cardinal, as emblematic of his support to the church. [Obs.] Skelton.
3. 4.(Man.) The center of the volta, ring, or manege ground, around which a horse turns. From pillar to post, hither and thither; to and fro; from one place or predicament to another; backward and forward. [Colloq.] -- Pillar saint. See Stylite. -- Pillars of the fauces. See Fauces, 1.
4. 5.Having a support in the form of a pillar, instead of legs; as, a pillar drill.