factionary

1. not comparableobsoleteBelonging to a faction; partisan; taking sides.

   Prithee, fellow, remember my name is Menenius, always factionary on the party of your general.

   c. 1608–1609 (date written), William Shakespeare, “The Tragedy of Coriolanus”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act V, scene ii]

plural factionaries

1. A member of a faction.

   1832, Walter Scott, Count Robert of Paris in Tales of My Landlord, Edinburgh: Robert Cadell, 4th Series, Volume 2, Chapter 10, p. 257, […] the traitor Ursel, some of them suppose, is dead, but if it were so, his name is sufficient to draw together his old factionaries […]

   2 more examples

   1555, Richard Eden (translator), The decades of the newe worlde or west India conteynyng the nauigations and conquestes of the Spanyardes by Peter Martyr d'Anghiera, London: Edwarde Sutton, Decade 2, Book 6, [p. 71b], Vaschus him selfe dyd greatly affecte this embasage: But neyther woolde the resydewe of his felowes electe hym therto, nor his factionaries suffer hym to departe: Aswell for that therby they thought they shulde bee left desolate, as also that they murmured that if Vaschus shulde once goo from theym, he wolde neuer returne to suche turmoyles and calamities […]

   He was a Cromwellian who never fought in the Civil War, a monarchist who denounced the corruptions of kingship, a servant of two hostile parties, and a factionary of neither, a politician who did his best for both worlds.

   1922, H. J. Massingham, “Andrew Marvell”, in William H. Bagguley, editor, Andrew Marvell, 1621-1678: Tercentenary Tributes, Oxford University Press, page 108