Source : Webster's Revised Unabridged Dictionary (1913)

Caucus \Cau"cus\, n. [Etymology uncertain. Mr. J. H. Trumbull
   finds the origin of caucus in the N. A. Indian word
   cawcawwassough or ca['u] 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].

Caucus \Cau"cus\, v. i. [imp. & p. p. {Caucused}; p. pr. & vb.
   n. {Caucusing}.]
   To hold, or meet in, a caucus or caucuses.

Source : WordNet®

caucus
     n : a closed political meeting
     v : meet to select a candidate or promote a policy