bastion

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A projecting part of a fortification.
2. n. A well-fortified position.
3. n. One that is considered similar to a defensive stronghold: You are a bastion of strength. See Synonyms at bulwark.

Century Dictionary and Cyclopedia

1. n. In fortification, a mass of earth, faced with sods, brick, or stones, standing out from a rampart, of which it is a principal part. A bastion consists of two flanks, each commanding and defending the adjacent curtain, or that portion of the wall extending from one bastion to another, and two faces making with each other an acute angle called the salient angle, and commanding the outworks and ground before the fortification. The inner space between the two flanks is the gorge, or entrance into the bastion. The use of the bastion is to bring every point at the foot of the rampart as much as possible under the guns of the place. Formerly called bulwark.

Wiktionary

1. n. a projecting part of a rampart or other fortification
2. n. a well-fortified position; a stronghold or citadel
3. n. figuratively a person, or thing, who strongly defends some principle

GNU Webster's 1913

1. n. (Fort.) A work projecting outward from the main inclosure of a fortification, consisting of two faces and two flanks, and so constructed that it is able to defend by a flanking fire the adjacent curtain, or wall which extends from one bastion to another. Two adjacent bastions are connected by the curtain, which joins the flank of one with the adjacent flank of the other. The distance between the flanks of a bastion is called the gorge. A lunette is a detached bastion. See ravelin.

WordNet 3.0

1. n. a stronghold into which people could go for shelter during a battle
2. n. projecting part of a rampart or other fortification
3. n. a group that defends a principle