factionary

Belonging to a faction; partisan; taking sides.

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

A member of a faction.

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 […]

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 […]