Zwing·li (zw?ng?l?, sw?ng?-, tsv?ng?-), Ulrich or Huldreich 1484-1531. Swiss religious reformer whose sermons on the absolute authority of the Bible (1519) marked the beginning of the Reformation in Switzerland.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.