Noun

1. A meeting, especially a preliminary meeting, of persons belonging to a party, to nominate candidates for public office, or to select delegates to a nominating convention, or to confer regarding measures of party policy; a political primary meeting.
2. A grouping of all the members of a legislature from the same party.

Verb

1. To meet in caucus.

   November 13, 2006, Associated Press, (reprinted in the Boston Globe) http://www.boston.com/news/nation/washington/articles/2006/11/13/lieberman_wont_rule_out_gop_caucusing/

   "Senator Joseph I. Lieberman of Connecticut said yesterday that he will caucus with Senate Democrats in the new Congress, but he would not rule out switching to the Republican caucus if he starts to feel uncomfortable among Democrats."