Wordorigins.org

The online OED has just published another quarterly update, revising the entries from quittal to ramvert. New words added to the dictionary include subprime, adj.; wantaway, adj.; cookie cutter, n. & adj.; and radiophysics, n.¹; this last referring to branch of physics dealing with ionizing radiation; the original entry, which is now radiophysics, n.², refers to the physics of radio waves.

Editor John Simpson comments on the changes here.

This name for the American South first appears in 1859 in the lyrics of a minstrel song. The etymology is uncertain, but it is most likely a reference to the Mason-Dixon Line, the border between Pennsylvania and Maryland delimited by those eponymous surveyors.

The first recorded use of the of Dixie is from the song Johnny Roach, by Daniel D. Emmett, first performed in February 1859:

Gib me de place called Dixie land,
Wid hoe and shubble in my hand.

Deadline is currently almost exclusively used to mean a time by which a task must be accomplished, but this was not always so. In the past, deadline had a variety of meanings, all related to a boundary for which there was a severe penalty for crossing.

The oldest of these uses dates to the American Civil War and refers to a line drawn around a military prison outside of which a prisoner could be shot, a literal “dead” line. From the Congressional Record of 12 January 1864:

The “dead line,” beyond which the prisoners are not allowed to pass.

A caucus is a meeting in which leaders and insiders set the agenda and policy of a larger organization or select candidates for office. It also can be used as a verb meaning to meet in a caucus.

The etymology is uncertain and there are several competing hypotheses. It has been claimed to date to before 1736, but the first recorded use of the term is from 1763 in John Adams’s diary:

This day learned that the caucus club meets, at certain times, in the garret of Tom Dawes.

This term is American, but of unknown origin, referring to a vague system of merit points used to curry favor with some authority. Anecdotal evidence indicates that it was part of military slang during WWII, but the earliest known use in print is from the Los Angeles Times of 15 March 1951:

You don’t know about brownie points? All my buddies keep score. In fact every married male should know about ‘em. It’s a way of figuring where you stand with the little woman—favor or disfavor. Started way back in the days of the leprechauns, I suppose, long before there were any doghouses.