Groot. Geert (Lat. Gerhardus Magnus), was born at Deventer in 1340, studied in Paris, and subsequently taught philosophy and theology in Cologne. Being possessed of a considerable property and of several prebends, he abandoned himself to a luxurious life, from which he was recalled by a serious sickness and the impressive exhortations of a friend, the Carthusian Henry Aeger. Thoroughly reformed, he entered the monastery of Monkhuysen, near Antwerp; but he left it again after three years, in order to become a travelling preacher. In union with Florence Radwyn, he established at Deventer the Society of the Brethren of Common Life, which was sanctioned in 1376 by Gregory XI. He died at Deventer of the plague, August 20, 1384. He wrote De Veridica Predicatione Evangelii : — De Sacris Libris Studendis (both in Kem-pis, Opera, t. iii). Thirty-three treatises of his remain in MS. See Ullmann, Reformers before the Reformation, vol. i; Bohringer, Kirche Christ;, vol. iti pt. iii, p. 612-644; Hoefer, Nouv. Biog. Generale, s.v. Groot.