Captain America: Civil War is a hit film at the early summer box office, having recently surpassed 1 billion dollars in worldwide ticket sales. The film raises a lot of questions, like whether you are on Captain America or Iron Man's side in a philosophical disagreement that escalates to a full-scale battle.

A lot of the questions related to the plot will most likely be answered in the two-part Avengers: Infinity War, the first part of which is scheduled for release in May 2018. However, a more basic question can be answered well before that having to do with the language of the title: How can a War be Civil?

This question has been asked before, most humorously by the late comedian George Carlin who noted that politeness and the brutality of war don't belong anywhere near one another, least of all next to each other in the same phrase.

So how did a word that shows up in phrases like civil discourse, which often characterizes respectful disagreement, or the admonition be civil!, which can chastise someone for everything from talking too loudly to using a tablecloth as a napkin, become associated with war—the least polite, least civil, activity of all?

Carlin's, and our, puzzlement at the civility of armed combat comes from a mixing of two separate senses of the word civil. The older meaning, the one present in civil war, dates from the late 14th century and means, "pertaining to the internal affairs of a state." So a civil war is a battle among citizens within a community, whether it is a community of Americans in the 1860s or a community of Avengers on the movie screen.

The second definition of civil, meaning "polite" arose later than the "affairs of state" definition—the former not being attested in English until the late 16th century, although the sense of "polite" was apparently always present in the Classical Latin source. The "polite" definition intersects with the "citizen" definition in an interesting way. It was once held that citizens were courteous and well mannered, as opposed to those in the military, who were considered impolite. So a word to describe a member of a community, a citizen, or, to use another word that comes to designate a non-soldier, a civilian, came to take on the meaning of qualities associated with those people. This process is one way that a single word can encompass two definitions that seem very different.

The word civil has had a long history apart from its presence in civil war. The civil disobedience of civil rights movements both in America and abroad demonstrated the effectiveness of not resorting to violence, and these movements, led by people like Gandhi and The Reverend Dr. Martin Luther King, Jr., demanded, in a relatively polite manner, freedom from injustice.

The recent coinage civil union uses the definition of civil that involves the internal workings of a community. Civil Union is first attested in 2000 and has become a term designating a state-recognized partnership that isn't officially a marriage. Opponents of same-sex marriage often proposed civil unions as an alternative arrangement when dealing with the opposition, who were demanding the right to marry and have those marriages hold the same status as traditional marriages and be fully recognized by the state. However, talk of civil unions has faded since the Supreme Court decision legalizing same-sex marriage (Obergefell vs. Hodges).

Whether it is about unions or the war over The Union, the tension between the two definitions of civil cannot be denied. It is important, in a time of increased animosity and vilification of those that disagree, to remember to remain civil when dealing with civil matters.