1. Any of the emperors of the Holy Roman Empire (962-1806), of Austria (1806-1918), or of Germany (1871-1918).
2. Used as the title for such a man.

[German, from Middle High German keiser, from Old High German keisar, from Latin Caesar. See caesar.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.