1. (n.) A carpentry obstruction, stockade, or other obstacle made in a passage in order to stop an enemy.

2. (n.) A fortress or fortified town, on the frontier of a country, commanding an avenue of approach.

3. (n.) A fence or railing to mark the limits of a place, or to keep back a crowd.

4. (n.) An any obstruction; anything which hinders approach or attack.

5. (n.) Any limit or boundary; a line of separation.

abatis advanced work arch dam backstop balistraria balustrade bamboo curtain bank banquette bar barbed-wire entanglement barbican barrage barricade bartizan bastion battlement bear-trap dam beaver dam blank wall blind alley blind gut block blockade blockage bolt boom bottleneck boundary brattice breakwater breastwork brick wall buffer buffer state bulkhead bulwark bumper casemate cecum cheval-de-frise choking choking off circumvallation clog cloison cofferdam collision mat congestion constipation contravallation costiveness counterscarp cul-de-sac curtain cushion dam dead end defense demibastion diaphragm dike dissepiment ditch dividing line dividing wall division drawbridge earthwork embankment embolism embolus enclosure entanglement escarp escarpment fence fender fieldwork fortalice fortification frontier gate glacis gorge gravity dam groin ha-ha hindrance hydraulic-fill dam impasse impediment infarct infarction interseptum iron curtain jam jetty leaping weir levee limit lock logjam loophole lunette machicolation mantelet mat merlon midriff midsection milldam moat mole mound obstacle obstipation obstruction outwork pad padlock palisade panel parados parapet paries partition party wall portcullis postern gate property line rail railing rampart ravelin redan redoubt roadblock rock-fill dam sally port scarp sconce sealing off seawall separation septulum septum shock pad shutter dam stockade stone wall stop stoppage strangulation tenaille vallation vallum wall weir wicket dam work