What’s the difference between the military and a militia? The distinction is generally between formal and regular service members and auxiliary or irregular personnel, but the latter term is less precise.
More precisely and comprehensively, the military is the entirety of a country’s designated personnel, matériel (as opposed to materials), and infrastructure as organized for defense. A militia can be a subcategory of the military, consisting of personnel generally deployed only during emergencies — though in some nations, the term refers to all citizens eligible to be called to military service — but it may refer, alternatively, to reserve forces, law-enforcement entities, or privately financed and equipped groups.
Both words are derived from the Latin term miles, meaning “soldier”: military stems from militaris, meaning “of soldiers or war,” of “military service,” or “warlike,” and militia is a direct borrowing of a word meaning “military service, warfare.”
Paramilitary (the prefix means “related to” or “resembling”) refers to armed forces organized more or less according to military protocols but not necessarily official or authorized. The term, like militia, is ambiguous, as it could refer, depending on the context, to a body of armed personnel ranging in degrees of legitimacy from national police to guerrillas.
Other words descended from the Latin miles include militant, in noun form referring to a (usually unofficial) combatant or as an adjective meaning “fighting” or “aggressive” in both military and nonmilitary contexts, and militate. Both these words developed from the Latin word military “serve as a soldier,” but the latter acquired a connotation of “counteract” or “have a negative effect on.”
In the United States, the military consists of the following branches of the armed forces: the US Army, the US Navy, the US Marine Corps, and the US Air Force; in time of war, the US Coast Guard can be attached to the navy. Subsidiary elements, considered militia, include the Army National Guard and the Air National Guard, plus the Army Reserve, the Navy Reserve, the Marine Corps Forces Reserve, the Air Force Reserve, and the Coast Guard Reserve, which collectively constitute the National Guard of the United States.