uniter

noun

1. (agent, form-of)Agent noun of unite; one who unites.

   “1892, Walt Whitman, "Out of the Cradle Endlessly Rocking," Leaves of Grass (abridged reprint of the 1892 edition), New York: The Modern Library, 1921, p. 213, https://archive.org/details/leavesofgrass00whit I, chanter of pains and joys, uniter of here and hereafter, / Taking all hints to use them, but swiftly leaping beyond them, / A reminiscence sing.”

   “The couple were congratulated by the witnesses and their uniter, the three of whom drank their health.”

   “It has been the most important traditional rôle of this country that it should act as a great uniter of the nations in that cultural fashion. We are the motherland of what is incomparably the most important language of the world and we have, to our glory, one of the greatest literatures of the world.”