army

An army is a military branch made up of specially trained people who serve their country in times of war and peace. (noun)

The men and women who volunteer to train and serve the United States of America are an example of an army.

An army is a lot of something. (noun)

A large group of ants is an example of an army.

An army is a group of people who work together for something they all believe in. (noun)

An example of an army is all the people needed to help support a political candidate who runs for office.

See army in Webster's New World College Dictionary

noun pl. armies

a large, organized body of soldiers for waging war, esp. on land
a military unit, usually two or more army corps, together with auxiliary troops
standing army
a large organization of persons for a specific cause: the Salvation Army
any large number of persons, animals, etc. considered as a whole: the army of the unemployed

See army in American Heritage Dictionary 4

(ärˈmē)

noun pl. ar·mies

a. A large body of people organized and trained for land warfare.
b. often Army The entire military land forces of a country.
c. A tactical and administrative military unit consisting of a headquarters, two or more corps, and auxiliary forces.
A large group of people organized for a specific cause: the construction army that built the Panama Canal.
A multitude; a host: An army of waiters served at the banquet. See Synonyms at multitude.