Philip, you are correct that it is a slur previously unknown. In that Washington Post story you linked to, the photo caption drops any nuance about the word: “Sen. George Allen had called S.R. Sidarth, a staffer of foe James Webb’s, a ‘macaca,’ a racial slur.“ If you have to look up the word to determine if it is a racial slur in some parts of the world, it probably isn’t that offensive.
