Jesuit a member of the Society of Jesus, a Roman Catholic order of priests founded by St Ignatius Loyola, St Francis Xavier, and others in 1534, to do missionary work. The order was zealous in opposing the Reformation. Despite periodic persecution it has retained an important influence in Catholic thought and education.
By their enemies the Jesuits were accused of teaching that the end justifies the means, and the lax principles of casuistry put forward by a few of their moralists were ascribed to the order as a whole, thus giving rise to jesuitical in the sense dissembling or equivocating, in the manner once associated with Jesuits.
Jesuits' bark an archaic term for cinchona bark, introduced into Europe from the Jesuit Missions in South America.

Jes·u·it / ˈjezhoōit; ˈjez(y)oō-/ • n. a member of the Society of Jesus, a Roman Catholic order of priests founded by St. Ignatius Loyola, St. Francis Xavier, and others in 1534, to do missionary work. The order was zealous in opposing the Reformation. Despite periodic persecution it has retained an important influence in Catholic thought and education.

Jesuit XVI. — F. Jésuite or modL. Jēsuīta, f. Jēsūs + -īta -ITE.
Hence Jesuitical XVI.