Soldier

A soldier is one who fights as part of an organized land-based armed force; if that force is for hire the person is generally termed a mercenary soldier, or mercenary. The majority of cognates of the word "soldier" that exist in other languages have a meaning that embraces both commissioned and non-commissioned officers in national land forces.

Etymology
The word soldier entered modern English in the 14th century from the equivalent Middle English word soudeour, from Anglo-French soudeer or soudeour, meaning mercenary, from soudee, meaning shilling's worth or wage, from sou or soud, shilling. The word is also related to the Medieval Latin soldarius, meaning soldier (literally, "one having pay"). These words ultimately derive the Late Latin word solidus, referring to an Ancient Roman coin used in the Byzantine Empire.

Occupational designations
In most armed forces use of the word 'soldier' has taken on a more general meaning due to the increasing specialization of military occupations that require different areas of knowledge and skill-sets. As a result, 'soldiers' are referred to by names or ranks which reflect an individual's military occupation specialty arm, service, or branch of military employment, their type of unit, or operational employment or technical use such as: trooper, tanker, commando, dragoon, infantryman, marine, paratrooper, ranger, sniper, engineer, sapper, medic, or a gunner.

Other terms
In many countries soldiers serving in specific occupations are referred to by terms other than their occupational name. For example military police personnel in the UK are known as "redcaps" from the colour of their berets or other headwear.

In the United States Army (or Marine Corps), infantrymen are sometimes called "grunts", while Army artillerymen are sometimes referred to as "redlegs", from the service branch color for artillery. US soldiers are often called "G.I.s". Members of the United States Marine Corps are typically referred to as "Marines" and not "soldiers".

French Marine Infantry are called marsouins (porpoises) because of their amphibious role. Military units in most armies have nicknames of this type, arising either from items of distinctive uniform, some historical connotation or rivalry between branches or regiments.

Career soldiers and conscripts
Some soldiers, such as conscripts or draftees, serve a single limited term. Others choose to serve until retirement; then they receive a pension and other benefits. In the USA, servicemembers can retire after 20 years. In other services, 30 years (hence the term "30-year man").