| Great Britain | refers to the island of England, Wales and Scotland, and its surrounding isles, but not Northern Ireland - 'Britain' for short |
| Great War | the term used to describe World War I by the generation that lived through it - also 'First World War' |
| green line | a line of demarcation between two enemies in a conflict |
| gross domestic product (GDP) | the total value of goods and services produced by a nation in a year |
| hardtack | a hard, flat, saltless biscuit that formed part of navy or army rations |
| heave to | to stop moving forward, especially a ship or vessel |
| heliograph | an instrument with mirrors and a shutter used for sending messages in Morse code by reflecting the sun's rays |
| home front | the country where civilians live |
| howitzer | a large gun with a short barrel that fires shells high up into the air so that they drop down onto a target |
| in perpetuity | describes as action or activity that's intended to last forever |
| incendiary | describes a weapon designed to cause a small fire; dropped together from aircraft to cause widespread damage |
| indemnity | an amount of money paid to someone because of some damage or loss they have suffered |
| infantry | soldiers who fight on foot |
| internee | a person put in prison for political reasons, especially an enemy citizen during wartime or a terrorism suspect |
| internment | the practice of putting people, usually civilians, in prison for political reasons, especially enemy foreign nationals during wartime or terrorism suspects |
| jaunty | naval slang for the master-at-arms, a senior sailor responsible for good order and discipline |
| kamikaze | An attack on an enemy where the actor knows that they will be killed doing it |
| light case | patient with lower-grade wounds or illness |
| lighter | a flat-bottomed barge used for transporting cargo, especially to load or unload a ship |
| mackintosh | a waterproof material made by cementing layers of cloth with rubber |
| mandate | the authority to carry out a particular policy or task as a result of winning an election or vote |
| mateship | comradeship of friends, usually male, viewed as an institution |
| medic | a doctor who works with the armed forces, as part of a medical corps |
| merchant ship | a ship that is part of a country's commercial shipping fleet, involved in transporting goods or carrying passengers; also known as a 'merchantman' |
| militia | a group that operates like an army but whose members are not professional soldiers |
| mine | a bomb hidden in the ground or in water that explodes when something touches it |
| minelayer | a warship or aircraft designed for the carrying and laying of mines |
| mobilisation | to prepare a military forces for a conflict |
| mobilise | to prepare a military forces for a conflict |
| Morse code | a telegraph code used for sending messages |
| musketry | the technique of using small arms |
| mustard gas | a chemical weapon used during World War I that caused blistering, sore eyes and internal injuries |
| muzzle velocity | the speed of a projectile as it leaves a gun's muzzle |
| neutral | describes a country that does not support any belligerent in a war or conflict |
| no-man's-land | an area of land that is not controlled by any side during a battle |
| obelisk | a tall stone pillar built to commemorate a person or an important event |
| objective | a place or position towards which forces are directed |
| occupation | the control of a territory by a foreign military power |
| offensive | a carefully planned attack made by a large formation or group of soldiers |
| Order of Battle | the units, formation and equipment of a military force; might include its identification, strength and command structure, and the disposition of the personnel |
| Ottoman Empire | the former Turkish empire in Europe, Asia and Africa, from the late 13th century until the end of World War I |
| outflank | to go around the flank of an opposing army by moving past it so it can be attacked from the side |
| outpost | a small group of buildings used for military purposes in a distant part of the country or in a foreign country |
| palliasse | a straw-filled mattress |
| parapet | a low wall along the edge of a tall structure, such as a bridge or roof |
| periscope | a vertical tube inside a submarine that lets a person see above the surface of the water |
| pillbox | a small building made of concrete used to defend a place in a battle |
| pinnace | a small boat carried on a large ship, used to carry goods and people from the ship to the shore |
| plateau | a large area of high and fairly flat land |
| plebiscite | a direct vote by the people of a country or region in which they say whether they agree or disagree with a particular policy |