Merriam-Webster Collegiate Dictionary - army

 noun  (plural armies)  Etymology: Middle English armee, from Anglo-French, from Medieval Latin armata — more at armada  Date: 14th century  1.  a. a large organized body of armed personnel trained for war especially on land  b. a unit capable of independent action and consisting usually of a headquarters, two or more corps, and auxiliary troops  c. often capitalized the complete military organization of a nation for land warfare  2. a great multitude an ~ of birds  3. a body of persons organized to advance a cause