caucus noun [Etymology uncertain. Mr. J. H. Trumbull finds the origin of caucus in the N. A. Indian word cawcawwassough or caú cau-as’u one who urges or pushes on, a promoter. See citation for an early use of the word caucus.]

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.

This day learned that the caucus club meets, at certain times, in the garret of Tom Dawes, the adjutant of the Boston regiment. John Adams's Diary [Feb. , 1763]

Cau′cus intransitive verb [imperfect or past participle Caucused; present participle or verbal noun Caucusing.]

To hold, or meet in, a caucus or caucuses.

-- Webster's unabridged 1913