Complex sentence: Conservative bishops in the Council were fearful that the idea of the College of Bishops would be interpreted as a new conciliarism, a fifteenth-century idea that an ecumenical council was the supreme authority under Christ in the Catholic Church.
Split into simpler sentences: Conservative bishops in the Council were fearful that the idea of the College of Bishops would be interpreted as a new conciliarism. Conciliarism was a fifteenth century idea that an ecumenical council was the supreme authority under Christ in the Catholic Church.