Britannica Academic Edition contains the Encyclopaedia Britannica, one of the largest, most authoritative encyclopedias in the world. Besides articles it includes ebooks, links to major news stories from the New York Times and the BBC, maps, photos, and other multi-media tools such as interactive timelines and videos. It also has Merriam-Webster’s Collegiate Dictionary and Thesaurus, and the Britannica Student Encyclopedia.
Blackwell Encyclopedia of Modern Christian Thought (Online) by 
The Encyclopedia of Christianity
Concise Sacramentum Mundi
Oxford Encyclopedia of the Reformation (Online) by 
Twentieth Century Encyclopedia of Catholicism
Sacramentum mundi: an encyclopedia of theology / edited by Karl Rahner ... [et al.]Concise Sacramentum Mundi
The Catholic Encyclopedia, also referred to today as the Old Catholic Encyclopedia and the Original Catholic Encyclopedia was published in the United States. The first volume appeared in March 1907 and it was completed in April 1914. It was designed "to give its readers full and authoritative information on the entire cycle of Catholic interests, action and doctrine.
It also offers in-depth portrayals of historical and philosophical ideas, persons and events, from the Roman Catholic point of view. On issues that divide Catholicism from other churches and Protestant ecclesiastic communities, the text consistently presents matters from the Catholic point of view. Since the encyclopedia was first undertaken in 1913 and has never been updated, many of its entries are out of date either with respect to the wider culture or to the Catholic ecclesiastical world. In particular it predates the creation of the Vatican City State and the Second Vatican Council (1962–1965), which introduced many significant changes in Catholic practice. (Adapted from Catholic Answers Web Site).
The Catholic Encyclopedia. Robert Appleton Co., 1907-1912. by 
101 key terms in philosophy and their importance in theology
Dictionary of fundamental theology / edited by Rene Latourelle, Rino Fisichella.
Dictionary of Latin and Greek Theological Terms
Dictionary of the Council. Edited by J. Deretz and A. Nocent.
Dictionary of Theology. By Karl Rahner and Herbert Vorgrimler
Saint Mary's Press glossary of theological terms / John T. Ford.
The Oxford dictionary of the Christian Church Online
Westminster Dictionary of Theological Terms
Westminster Dictionary of Christian Theology
The Oxford Companion to Christian Thought
