Source : Webster's Revised Unabridged Dictionary (1913)

Bastion \Bas"tion\, n. [F. bastion (cf. It. bastione), fr. LL.
   bastire to build (cf. F. b?tir, It. bastire), perh. from the
   idea of support for a weight, and akin to Gr. ? to lift,
   carry, and to E. baston, baton.] (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}.

Source : WordNet®

bastion
     n 1: a group that defends a principle; "a bastion against
          corruption"; "the last bastion of communism"
     2: a stronghold into which people could go for shelter during a
        battle [syn: {citadel}]
     3: projecting part of a rampart or other fortification