The word "casualty" refers to those listed as killed, wounded and or missing. The acronym for these are: Kia- Killed in Action, WIA- Wounded in Action, MIA- Missing in Action.
It refers to the two types of casualty in a battle or war. For instance, there might be 1000 casualties, wounded and dead, of whom 200 might be killed and 800 wounded.
In most common usage, casualties refers to people who are 'put out of action' , wounded, maimed or killed, by intent or by accident.
100s of Spartans were killed in many places, but the question probably refers to the Battle of Thermopylae in 480 BC, and the legend of the 300 Spartans.
I presume the question refers to the massacre which took place in 1890 at Wounded Knee in South Dakota and effectively marked the end of the US army's campaign to force native American tribes onto reservations established by the government.
Battle execution refers to the commencement of battle.
THere was never a person called "Wounded Knee".The famous massacre that took place in December 1890 was not named for a person but for a small creek nearby - chankpé opi wakpála or Wounded Knee Creek in Lakota. This name existed long before the battle took place and probably refers to a long-ago fight between the Lakotas and another tribe such as the Crows, when a warrior on one side was wounded by an arrow in the knee.
The Holocaust
"Casualty" refers to a person who is killed or injured. "Fatality" refers specifically to a person who is killed.
The Battle of Lexington.
The "battle" or "massacre" takes its name from a nearby creek, called chankpe opi wakpala in Lakota. This name, meaning "the creek of a wounded knee", was given to the stream (a tributary of White River) long before the battle, so it does not refer to any wound received during that famous encounter.It more likely refers to some much earlier fight between the Lakota and another tribe (perhaps the Crows).
The Battle of Concord refers to when the British marched into Concord on 19 April 1775, searching for stores hidden by the members of the rebellion. They destroyed a few items. A small group of British went out to the North Bridge, where they were approached by Minutemen from Acton and Bedford. The British began to detroy the bridge so they could not cross it and follow them. Then firing commenced and some British were wounded and killed. This "skirmish" did not last very long, probably only a few minutes. The British return march to Boston started a running battle that lasted most of the afternoon and resulted in many more casualties.
It is a common noun, unless it refers to a specific battle: for example, the Battle of the Little Bighorn.