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The Collaborative International Dictionary
Demibastion

Demibastion \Dem"i*bas"tion\ (?; 106), n. [Cf. F. demi- bastion.] (Fort.) A half bastion, or that part of a bastion consisting of one face and one flank.

Wiktionary
demibastion

n. (context military English) A half bastion, or that part of a bastion consisting of one face and one flank.