There are a number of useful glossaries of liturgy and church terms available online. Here are a few of them:
Alphabetical Listing of Glossary of Church Terms - On the United States Conference of Catholic Bishops
Glossary of Catholic Terms & Terminology used in the Catholic Church - Catholic Archdiocese of Johannesburg
Common Liturgical Terms from the Diocese of Greensburg, based on Dennis C. Smolarski's Liturgical Literacy (Paulist Press, 1990)
Glossary of Liturgical Terms from Fr. Tom Richstatter, O.F.M. professor of Liturgy and Sacramental Theology in St. Meinrad's Archabbey's School of Theology
Glossary of Terms - On the Web site of Diocese of Maitland-Newcastle. definitions have been taken from The Collins Dove Dictionary for Young Catholics, Laurie Woods (Ed.), Melbourne, 1990.
Also see my earlier posting on Catholic Dictionaries.